path: root/indra/llcommon/llinitparam.h

/**
 * @file llinitparam.h
 * @brief parameter block abstraction for creating complex objects and
 * parsing construction parameters from xml and LLSD
 *
 * $LicenseInfo:firstyear=2008&license=viewerlgpl$
 * Second Life Viewer Source Code
 * Copyright (C) 2010, Linden Research, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation;
 * version 2.1 of the License only.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
 * $/LicenseInfo$
 */

#ifndef LL_LLPARAM_H
#define LL_LLPARAM_H

#include <vector>
#include <list>
#include <boost/function.hpp>
#include <boost/type_traits/is_convertible.hpp>
#include <boost/type_traits/is_enum.hpp>
#include <boost/unordered_map.hpp>

#include "llerror.h"
#include "llstl.h"
#include "llpredicate.h"
#include "llsd.h"

namespace LLTypeTags
{
    template <typename INNER_TYPE, int _SORT_ORDER>
    struct TypeTagBase
    {
        typedef void        is_tag_t;
        typedef INNER_TYPE  inner_t;
        static const int    SORT_ORDER=_SORT_ORDER;
    };

    template <int VAL1, int VAL2>
    struct GreaterThan
    {
        static const bool value = VAL1 > VAL2;
    };

    template<typename ITEM, typename REST, bool NEEDS_SWAP = GreaterThan<ITEM::SORT_ORDER, REST::SORT_ORDER>::value >
    struct Swap
    {
        typedef typename ITEM::template Cons<REST>::value_t value_t;
    };

    template<typename ITEM, typename REST>
    struct Swap<ITEM, REST, true>
    {
        typedef typename REST::template Cons<Swap<ITEM, typename REST::inner_t>::value_t>::value_t value_t;
    };

    template<typename T, typename SORTABLE = void>
    struct IsSortable
    {
        static const bool value = false;
    };

    template<typename T>
    struct IsSortable<T, typename T::is_tag_t>
    {
        static const bool value = true;
    };

    template<typename ITEM, typename REST, bool IS_REST_SORTABLE = IsSortable<REST>::value>
    struct InsertInto
    {
        typedef typename ITEM::template Cons<REST>::value_t value_t;
    };

    template<typename ITEM, typename REST>
    struct InsertInto <ITEM, REST, true>
    {
        typedef typename Swap<ITEM, REST>::value_t value_t;
    };

    template<typename T, bool SORTABLE = IsSortable<T>::value>
    struct Sorted
    {
        typedef T value_t;
    };

    template<typename T>
    struct Sorted <T, true>
    {
        typedef typename InsertInto<T, typename Sorted<typename T::inner_t>::value_t>::value_t value_t;
    };
}

namespace LLInitParam
{
    // used to indicate no matching value to a given name when parsing
    struct Flag{};

    template<typename T> const T& defaultValue() { static T value; return value; }

    // wraps comparison operator between any 2 values of the same type
    // specialize to handle cases where equality isn't defined well, or at all
    template <typename T, bool IS_BOOST_FUNCTION = boost::is_convertible<T, boost::function_base>::value >
    struct ParamCompare
    {
        static bool equals(const T &a, const T &b)
        {
            return a == b;
        }
    };

    // boost function types are not comparable
    template<typename T>
    struct ParamCompare<T, true>
    {
        static bool equals(const T&a, const T &b)
        {
            return false;
        }
    };

    template<>
    struct ParamCompare<LLSD, false>
    {
        static bool equals(const LLSD &a, const LLSD &b) { return false; }
    };

    template<>
    struct ParamCompare<Flag, false>
    {
        static bool equals(const Flag& a, const Flag& b) { return false; }
    };


    // helper functions and classes
    typedef ptrdiff_t param_handle_t;
    struct IS_A_BLOCK {};
    struct NOT_BLOCK {};

    // these templates allow us to distinguish between template parameters
    // that derive from BaseBlock and those that don't
    template<typename T, typename BLOCK_IDENTIFIER = void>
    struct IsBlock
    {
        typedef NOT_BLOCK value_t;
    };

    template<typename T>
    struct IsBlock<T, typename T::baseblock_base_class_t>
    {
        typedef IS_A_BLOCK value_t;
    };

    // ParamValue class directly manages the wrapped value
    // by holding on to a copy (scalar params)
    // or deriving from it (blocks)
    // has specializations for custom value behavior
    // and "tag" values like Lazy and Atomic
    template<typename T, typename VALUE_IS_BLOCK = typename IsBlock<T>::value_t>
    class ParamValue
    {
        typedef ParamValue<T, VALUE_IS_BLOCK>   self_t;

    public:
        typedef T   default_value_t;
        typedef T   value_t;

        ParamValue(): mValue() {}
        ParamValue(const default_value_t& other) : mValue(other) {}

        void setValue(const value_t& val)
        {
            mValue = val;
        }

        const value_t& getValue() const
        {
            return mValue;
        }

        T& getValue()
        {
            return mValue;
        }

        bool isValid() const { return true; }

    protected:
        T mValue;
    };

    template<typename T>
    class ParamValue<T, IS_A_BLOCK>
    :   public T
    {
        typedef ParamValue<T, IS_A_BLOCK>   self_t;
    public:
        typedef T   default_value_t;
        typedef T   value_t;

        ParamValue()
        :   T()
        {}

        ParamValue(const default_value_t& other)
        :   T(other)
        {}

        void setValue(const value_t& val)
        {
            *this = val;
        }

        const value_t& getValue() const
        {
            return *this;
        }

        T& getValue()
        {
            return *this;
        }
    };


    // empty default implementation of key cache
    // leverages empty base class optimization
    template <typename T>
    class TypeValues
    :   public ParamValue<typename LLTypeTags::Sorted<T>::value_t>
    {
    private:
        struct Inaccessable{};
    public:
        typedef std::map<std::string, T> value_name_map_t;
        typedef Inaccessable name_t;
        typedef TypeValues<T> type_value_t;
        typedef ParamValue<typename LLTypeTags::Sorted<T>::value_t> param_value_t;
        typedef typename param_value_t::value_t value_t;

        TypeValues(const typename param_value_t::value_t& val)
        :   param_value_t(val)
        {}

        void setValueName(const std::string& key) {}
        std::string getValueName() const { return ""; }
        std::string calcValueName(const value_t& value) const { return ""; }
        void clearValueName() const {}

        static bool getValueFromName(const std::string& name, value_t& value)
        {
            return false;
        }

        static bool valueNamesExist()
        {
            return false;
        }

        static std::vector<std::string>* getPossibleValues()
        {
            return NULL;
        }

        void assignNamedValue(const Inaccessable& name)
        {}

        operator const value_t&() const
        {
            return param_value_t::getValue();
        }

        const value_t& operator()() const
        {
            return param_value_t::getValue();
        }

        static value_name_map_t* getValueNames() {return NULL;}
    };

    // helper class to implement name value lookups
    // and caching of last used name
    template <typename T, typename DERIVED_TYPE = TypeValues<T>, bool IS_SPECIALIZED = true >
    class TypeValuesHelper
    :   public ParamValue<typename LLTypeTags::Sorted<T>::value_t>
    {
        typedef TypeValuesHelper<T, DERIVED_TYPE, IS_SPECIALIZED> self_t;
    public:
        typedef typename std::map<std::string, T> value_name_map_t;
        typedef std::string name_t;
        typedef self_t type_value_t;
        typedef ParamValue<typename LLTypeTags::Sorted<T>::value_t> param_value_t;
        typedef typename param_value_t::value_t value_t;

        TypeValuesHelper(const typename param_value_t::value_t& val)
        :   param_value_t(val)
        {}

        //TODO: cache key by index to save on param block size
        void setValueName(const std::string& value_name)
        {
            mValueName = value_name;
        }

        std::string getValueName() const
        {
            return mValueName;
        }

        std::string calcValueName(const value_t& value) const
        {
            value_name_map_t* map = getValueNames();
            for (typename value_name_map_t::value_type& map_pair : *map)
            {
                if (ParamCompare<T>::equals(map_pair.second, value))
                {
                    return map_pair.first;
                }
            }

            return "";
        }

        void clearValueName() const
        {
            mValueName.clear();
        }

        static bool getValueFromName(const std::string& name, value_t& value)
        {
            value_name_map_t* map = getValueNames();
            typename value_name_map_t::iterator found_it = map->find(name);
            if (found_it == map->end()) return false;

            value = found_it->second;
            return true;
        }

        static bool valueNamesExist()
        {
            return !getValueNames()->empty();
        }

        static value_name_map_t* getValueNames()
        {
            static value_name_map_t sMap;
            static bool sInitialized = false;

            if (!sInitialized)
            {
                sInitialized = true;
                DERIVED_TYPE::declareValues();
            }
            return &sMap;
        }

        static std::vector<std::string>* getPossibleValues()
        {
            static std::vector<std::string> sValues;

            value_name_map_t* map = getValueNames();
            for (typename value_name_map_t::value_type& map_pair : *map)
            {
                sValues.push_back(map_pair.first);
            }
            return &sValues;
        }

        static void declare(const std::string& name, const value_t& value)
        {
            (*getValueNames())[name] = value;
        }

        void operator ()(const std::string& name)
        {
            *this = name;
        }

        void assignNamedValue(const std::string& name)
        {
            if (getValueFromName(name, param_value_t::getValue()))
            {
                setValueName(name);
            }
        }

        operator const value_t&() const
        {
            return param_value_t::getValue();
        }

        const value_t& operator()() const
        {
            return param_value_t::getValue();
        }

    protected:
        static void getName(const std::string& name, const value_t& value)
        {}

        mutable std::string mValueName;
    };

    // string types can support custom named values, but need
    // to disambiguate in code between a string that is a named value
    // and a string that is a name
    template <typename DERIVED_TYPE>
    class TypeValuesHelper<std::string, DERIVED_TYPE, true>
    :   public TypeValuesHelper<std::string, DERIVED_TYPE, false>
    {
    public:
        typedef TypeValuesHelper<std::string, DERIVED_TYPE, true> self_t;
        typedef TypeValuesHelper<std::string, DERIVED_TYPE, false> base_t;
        typedef std::string value_t;
        typedef std::string name_t;
        typedef self_t type_value_t;

        TypeValuesHelper(const std::string& val)
        :   base_t(val)
        {}

        void operator ()(const std::string& name)
    {
            *this = name;
        }

        self_t& operator =(const std::string& name)
        {
            if (base_t::getValueFromName(name, ParamValue<std::string>::getValue()))
            {
                base_t::setValueName(name);
            }
            else
            {
                ParamValue<std::string>::setValue(name);
            }
            return *this;
        }

        operator const value_t&() const
        {
            return ParamValue<std::string>::getValue();
        }

        const value_t& operator()() const
        {
            return ParamValue<std::string>::getValue();
        }

    };

    // parser base class with mechanisms for registering readers/writers/inspectors of different types
    class LL_COMMON_API Parser
    {
        LOG_CLASS(Parser);
    public:
        typedef std::vector<std::pair<std::string, bool> >                  name_stack_t;
        typedef std::pair<name_stack_t::iterator, name_stack_t::iterator>   name_stack_range_t;
        typedef std::vector<std::string>                                    possible_values_t;

        typedef bool (*parser_read_func_t)(Parser& parser, void* output);
        typedef bool (*parser_write_func_t)(Parser& parser, const void*, name_stack_t&);
        typedef boost::function<void (name_stack_t&, S32, S32, const possible_values_t*)>   parser_inspect_func_t;

        typedef std::map<const std::type_info*, parser_read_func_t>     parser_read_func_map_t;
        typedef std::map<const std::type_info*, parser_write_func_t>    parser_write_func_map_t;
        typedef std::map<const std::type_info*, parser_inspect_func_t>  parser_inspect_func_map_t;

    public:

        Parser(parser_read_func_map_t& read_map, parser_write_func_map_t& write_map, parser_inspect_func_map_t& inspect_map)
        :   mParseSilently(false),
            mParserReadFuncs(&read_map),
            mParserWriteFuncs(&write_map),
            mParserInspectFuncs(&inspect_map)
        {}

        virtual ~Parser();

        template <typename T> bool readValue(T& param, typename boost::disable_if<boost::is_enum<T> >::type* dummy = 0)
        {
            parser_read_func_map_t::iterator found_it = mParserReadFuncs->find(&typeid(T));
            if (found_it != mParserReadFuncs->end())
            {
                return found_it->second(*this, (void*)&param);
            }

            return false;
        }

        template <typename T> bool readValue(T& param, typename boost::enable_if<boost::is_enum<T> >::type* dummy = 0)
        {
            parser_read_func_map_t::iterator found_it = mParserReadFuncs->find(&typeid(T));
            if (found_it != mParserReadFuncs->end())
            {
                return found_it->second(*this, (void*)&param);
            }
            else
            {
                found_it = mParserReadFuncs->find(&typeid(S32));
                if (found_it != mParserReadFuncs->end())
                {
                    S32 int_value;
                    bool parsed = found_it->second(*this, (void*)&int_value);
                    param = (T)int_value;
                    return parsed;
                }
            }
            return false;
        }

        template <typename T> bool writeValue(const T& param, name_stack_t& name_stack)
        {
            parser_write_func_map_t::iterator found_it = mParserWriteFuncs->find(&typeid(T));
            if (found_it != mParserWriteFuncs->end())
            {
                return found_it->second(*this, (const void*)&param, name_stack);
            }
            return false;
        }

        // dispatch inspection to registered inspection functions, for each parameter in a param block
        template <typename T> bool inspectValue(name_stack_t& name_stack, S32 min_count, S32 max_count, const possible_values_t* possible_values)
        {
            parser_inspect_func_map_t::iterator found_it = mParserInspectFuncs->find(&typeid(T));
            if (found_it != mParserInspectFuncs->end())
            {
                found_it->second(name_stack, min_count, max_count, possible_values);
                return true;
            }
            return false;
        }

        virtual std::string getCurrentElementName() = 0;
        virtual std::string getCurrentFileName() = 0;
        virtual void parserWarning(const std::string& message);
        virtual void parserError(const std::string& message);
        void setParseSilently(bool silent) { mParseSilently = silent; }

    protected:
        template <typename T>
        void registerParserFuncs(parser_read_func_t read_func, parser_write_func_t write_func = NULL)
        {
            mParserReadFuncs->insert(std::make_pair(&typeid(T), read_func));
            mParserWriteFuncs->insert(std::make_pair(&typeid(T), write_func));
        }

        template <typename T>
        void registerInspectFunc(parser_inspect_func_t inspect_func)
        {
            mParserInspectFuncs->insert(std::make_pair(&typeid(T), inspect_func));
        }

        bool                mParseSilently;

    private:
        parser_read_func_map_t*     mParserReadFuncs;
        parser_write_func_map_t*    mParserWriteFuncs;
        parser_inspect_func_map_t*  mParserInspectFuncs;
    };

    class Param;

    enum ESerializePredicates
    {
        PROVIDED,
        REQUIRED,
        VALID,
        HAS_DEFAULT_VALUE,
        EMPTY
    };

    typedef LLPredicate::Rule<ESerializePredicates> predicate_rule_t;

    predicate_rule_t default_parse_rules();

    // various callbacks and constraints associated with an individual param
    struct LL_COMMON_API ParamDescriptor
    {
        struct UserData
        {
            virtual ~UserData() {}
        };

        typedef bool(*merge_func_t)(Param&, const Param&, bool);
        typedef bool(*deserialize_func_t)(Param&, Parser&, Parser::name_stack_range_t&, bool);
        typedef bool(*serialize_func_t)(const Param&, Parser&, Parser::name_stack_t&, const predicate_rule_t rules, const Param* diff_param);
        typedef void(*inspect_func_t)(const Param&, Parser&, Parser::name_stack_t&, S32 min_count, S32 max_count);
        typedef bool(*validation_func_t)(const Param*);

        ParamDescriptor(param_handle_t p,
                        merge_func_t merge_func,
                        deserialize_func_t deserialize_func,
                        serialize_func_t serialize_func,
                        validation_func_t validation_func,
                        inspect_func_t inspect_func,
                        S32 min_count,
                        S32 max_count);

        ParamDescriptor();
        ~ParamDescriptor();

        param_handle_t      mParamHandle;
        merge_func_t        mMergeFunc;
        deserialize_func_t  mDeserializeFunc;
        serialize_func_t    mSerializeFunc;
        inspect_func_t      mInspectFunc;
        validation_func_t   mValidationFunc;
        S32                 mMinCount;
        S32                 mMaxCount;
        S32                 mNumRefs;
        UserData*           mUserData;
    };

    typedef std::shared_ptr<ParamDescriptor> ParamDescriptorPtr;

    // each derived Block class keeps a static data structure maintaining offsets to various params
    class LL_COMMON_API BlockDescriptor
    {
    public:
        BlockDescriptor();

        typedef enum e_initialization_state
        {
            UNINITIALIZED,
            INITIALIZING,
            INITIALIZED
        } EInitializationState;

        void aggregateBlockData(BlockDescriptor& src_block_data);
        void addParam(ParamDescriptorPtr param, const char* name);

        typedef boost::unordered_map<const std::string, ParamDescriptorPtr>                     param_map_t;
        typedef std::vector<ParamDescriptorPtr>                                                 param_list_t;
        typedef std::list<ParamDescriptorPtr>                                                   all_params_list_t;
        typedef std::vector<std::pair<param_handle_t, ParamDescriptor::validation_func_t> >     param_validation_list_t;

        param_map_t                     mNamedParams;           // parameters with associated names
        param_list_t                    mUnnamedParams;         // parameters with_out_ associated names
        param_validation_list_t         mValidationList;        // parameters that must be validated
        all_params_list_t               mAllParams;             // all parameters, owns descriptors
        size_t                          mMaxParamOffset;
        EInitializationState            mInitializationState;   // whether or not static block data has been initialized
        class BaseBlock*                mCurrentBlockPtr;       // pointer to block currently being constructed
    };

        //TODO: implement in terms of owned_ptr
        template<typename T>
    class LazyValue
        {
        public:
        LazyValue()
                : mPtr(NULL)
            {}

        ~LazyValue()
            {
                delete mPtr;
            }

        LazyValue(const T& value)
            {
            mPtr = new T(value);
        }

        LazyValue(const LazyValue& other)
        :   mPtr(NULL)
                {
            *this = other;
                }

        LazyValue& operator = (const LazyValue& other)
                {
            if (!other.mPtr)
            {
                delete mPtr;
                    mPtr = NULL;
                }
            else
            {
                if (!mPtr)
                {
                    mPtr = new T(*other.mPtr);
                }
                else
                {
                    *mPtr = *(other.mPtr);
                }
                }
                return *this;
            }

        bool operator==(const LazyValue& other) const
        {
            if (empty() || other.empty()) return false;
            return *mPtr == *other.mPtr;
        }

            bool empty() const
            {
                return mPtr == NULL;
            }

            void set(const T& other)
            {
            if (!mPtr)
            {
                mPtr = new T(other);
            }
            else
            {
                *mPtr = other;
            }
        }

            const T& get() const
            {
            return *ensureInstance();
            }

            T& get()
            {
            return *ensureInstance();
        }

        operator const T&() const
        {
            return get();
            }

        private:
            // lazily allocate an instance of T
            T* ensureInstance() const
            {
                if (mPtr == NULL)
                {
                    mPtr = new T();
                }
                return mPtr;
            }

        private:

            mutable T* mPtr;
        };

    // root class of all parameter blocks

    class LL_COMMON_API BaseBlock
    {
    public:
        // lift block tags into baseblock namespace so derived classes do not need to qualify them
        typedef LLInitParam::IS_A_BLOCK IS_A_BLOCK;
        typedef LLInitParam::NOT_BLOCK NOT_A_BLOCK;

        template<typename T>
        struct Sequential : public LLTypeTags::TypeTagBase<T, 2>
        {
            template <typename S> struct Cons { typedef Sequential<ParamValue<S> > value_t; };
            template <typename S> struct Cons<Sequential<S> > { typedef Sequential<S> value_t; };
        };

        template<typename T>
        struct Atomic : public LLTypeTags::TypeTagBase<T, 1>
        {
            template <typename S> struct Cons { typedef Atomic<ParamValue<S> > value_t; };
            template <typename S> struct Cons<Atomic<S> > { typedef Atomic<S> value_t; };
        };

        template<typename T, typename BLOCK_T = typename IsBlock<T>::value_t >
        struct Lazy : public LLTypeTags::TypeTagBase<T, 0>
        {
            template <typename S> struct Cons
            {
                typedef Lazy<ParamValue<S, BLOCK_T>, BLOCK_T> value_t;
            };
            template <typename S> struct Cons<Lazy<S, IS_A_BLOCK> >
            {
                typedef Lazy<S, IS_A_BLOCK> value_t;
            };
            template <typename S> struct Cons<Lazy<S, NOT_A_BLOCK> >
            {
                typedef Lazy<S, BLOCK_T> value_t;
            };
        };

        // "Multiple" constraint types, put here in root class to avoid ambiguity during use
        struct AnyAmount
        {
            enum { minCount = 0 };
            enum { maxCount = U32_MAX };
        };

        template<U32 MIN_AMOUNT>
        struct AtLeast
        {
            enum { minCount = MIN_AMOUNT };
            enum { maxCount = U32_MAX };
        };

        template<U32 MAX_AMOUNT>
        struct AtMost
        {
            enum { minCount = 0 };
            enum { maxCount = MAX_AMOUNT };
        };

        template<U32 MIN_AMOUNT, U32 MAX_AMOUNT>
        struct Between
        {
            enum { minCount = MIN_AMOUNT };
            enum { maxCount = MAX_AMOUNT };
        };

        template<U32 EXACT_COUNT>
        struct Exactly
        {
            enum { minCount = EXACT_COUNT };
            enum { maxCount = EXACT_COUNT };
        };

        // this typedef identifies derived classes as being blocks
        typedef void baseblock_base_class_t;
        LOG_CLASS(BaseBlock);
        friend class Param;

        BaseBlock()
        :   mValidated(false),
            mParamProvided(false)
        {}

        virtual ~BaseBlock() {}
        bool submitValue(Parser::name_stack_t& name_stack, Parser& p, bool silent=false);

        param_handle_t getHandleFromParam(const Param* param) const;
        bool validateBlock(bool emit_errors = true) const;

        bool isProvided() const
        {
            return mParamProvided;
        }

        bool isValid() const
        {
            return validateBlock(false);
        }


        Param* getParamFromHandle(const param_handle_t param_handle)
        {
            if (param_handle == 0) return NULL;

            U8* baseblock_address = reinterpret_cast<U8*>(this);
            return reinterpret_cast<Param*>(baseblock_address + param_handle);
        }

        const Param* getParamFromHandle(const param_handle_t param_handle) const
        {
            const U8* baseblock_address = reinterpret_cast<const U8*>(this);
            return reinterpret_cast<const Param*>(baseblock_address + param_handle);
        }

        void addSynonym(Param& param, const std::string& synonym);

        // Blocks can override this to do custom tracking of changes
        virtual void paramChanged(const Param& changed_param, bool user_provided)
        {
            if (user_provided)
            {
                // a child param has been explicitly changed
                // so *some* aspect of this block is now provided
                mValidated = false;
                mParamProvided = true;
            }
        }

        bool deserializeBlock(Parser& p, Parser::name_stack_range_t& name_stack_range, bool new_name);
        bool serializeBlock(Parser& p, Parser::name_stack_t& name_stack, const predicate_rule_t rule, const BaseBlock* diff_block = NULL) const;
        bool inspectBlock(Parser& p, Parser::name_stack_t name_stack = Parser::name_stack_t(), S32 min_count = 0, S32 max_count = S32_MAX) const;

        virtual const BlockDescriptor& mostDerivedBlockDescriptor() const { return getBlockDescriptor(); }
        virtual BlockDescriptor& mostDerivedBlockDescriptor() { return getBlockDescriptor(); }

        // take all provided params from other and apply to self
        bool overwriteFrom(const BaseBlock& other)
        {
            return false;
        }

        // take all provided params that are not already provided, and apply to self
        bool fillFrom(const BaseBlock& other)
        {
            return false;
        }

        ParamDescriptorPtr findParamDescriptor(const Param& param);

        // take all provided params from other and apply to self
        bool mergeBlock(BlockDescriptor& block_data, const BaseBlock& other, bool overwrite);

        static BlockDescriptor& getBlockDescriptor()
        {
            static BlockDescriptor sBlockDescriptor;
            return sBlockDescriptor;
        }

    protected:
        void init(BlockDescriptor& descriptor, BlockDescriptor& base_descriptor, size_t block_size);


        bool mergeBlockParam(bool source_provided, bool dst_provided, BlockDescriptor& block_data, const BaseBlock& source, bool overwrite)
        {
            return mergeBlock(block_data, source, overwrite);
        }

        mutable bool    mValidated; // lazy validation flag
        bool            mParamProvided;

    private:
        const std::string& getParamName(const BlockDescriptor& block_data, const Param* paramp) const;
    };

    class LL_COMMON_API Param
    {
    public:
        void setProvided(bool is_provided = true)
        {
            mIsProvided = is_provided;
            enclosingBlock().paramChanged(*this, is_provided);
        }

        Param& operator =(const Param& other)
        {
            mIsProvided = other.mIsProvided;
            // don't change mEnclosingblockoffset
            return *this;
        }
    protected:

        bool anyProvided() const { return mIsProvided; }

        Param(BaseBlock* enclosing_block);

        // store pointer to enclosing block as offset to reduce space and allow for quick copying
        BaseBlock& enclosingBlock() const
        {
            const U8* my_addr = reinterpret_cast<const U8*>(this);
            // get address of enclosing BLOCK class using stored offset to enclosing BaseBlock class
            return *const_cast<BaseBlock*>
                (reinterpret_cast<const BaseBlock*>
                    (my_addr - (ptrdiff_t)getEnclosingBlockOffset()));
        }

        U32 getEnclosingBlockOffset() const
    {
            return ((U32)mEnclosingBlockOffsetHigh << 16) | (U32)mEnclosingBlockOffsetLow;
        }

    private:
        friend class BaseBlock;

        //24 bits for member offset field and 1 bit for provided flag
        U16     mEnclosingBlockOffsetLow;
        U8      mEnclosingBlockOffsetHigh:7;
        U8      mIsProvided:1;

    };

    template<typename T, typename NAME_VALUE_LOOKUP = TypeValues<T> >
    struct ParamIterator
    {
        typedef typename std::vector<typename NAME_VALUE_LOOKUP::type_value_t >::const_iterator const_iterator;
        typedef typename std::vector<typename NAME_VALUE_LOOKUP::type_value_t >::iterator           iterator;
    };

    // wrapper for parameter with a known type
    // specialized to handle 4 cases:
    // simple "scalar" value
    // parameter that is itself a block
    // multiple scalar values, stored in a vector
    // multiple blocks, stored in a vector
    template<typename   T,
            typename    NAME_VALUE_LOOKUP = TypeValues<T>,
            bool        HAS_MULTIPLE_VALUES = false,
            typename    VALUE_IS_BLOCK = typename IsBlock<ParamValue<typename LLTypeTags::Sorted<T>::value_t> >::value_t>
    class TypedParam
    :   public Param,
        public NAME_VALUE_LOOKUP::type_value_t
    {
    protected:
        typedef TypedParam<T, NAME_VALUE_LOOKUP, HAS_MULTIPLE_VALUES, VALUE_IS_BLOCK>   self_t;
        typedef ParamValue<typename LLTypeTags::Sorted<T>::value_t>                     param_value_t;
        typedef typename param_value_t::default_value_t                                 default_value_t;
        typedef typename NAME_VALUE_LOOKUP::type_value_t                                named_value_t;
    public:
        typedef typename param_value_t::value_t                                         value_t;

        using named_value_t::operator();

        TypedParam(BlockDescriptor& block_descriptor, const char* name, const default_value_t& value, ParamDescriptor::validation_func_t validate_func, S32 min_count, S32 max_count)
        :   Param(block_descriptor.mCurrentBlockPtr),
            named_value_t(value)
        {
            if (LL_UNLIKELY(block_descriptor.mInitializationState == BlockDescriptor::INITIALIZING))
            {
                init(block_descriptor, validate_func, min_count, max_count, name);
            }
        }

        bool isProvided() const { return Param::anyProvided(); }

        bool isValid() const { return true; }

        static bool deserializeParam(Param& param, Parser& parser, Parser::name_stack_range_t& name_stack_range, bool new_name)
        {
            self_t& typed_param = static_cast<self_t&>(param);
            // no further names in stack, attempt to parse value now
            if (name_stack_range.first == name_stack_range.second)
            {
                std::string name;

                // try to parse a known named value
                if(named_value_t::valueNamesExist()
                    && parser.readValue(name)
                    && named_value_t::getValueFromName(name, typed_param.getValue()))
                {
                    typed_param.setValueName(name);
                    typed_param.setProvided();
                    return true;
                }
                // try to read value directly
                else if (parser.readValue(typed_param.getValue()))
                {
                    typed_param.clearValueName();
                    typed_param.setProvided();
                    return true;
                }
            }
            return false;
        }

        static bool serializeParam(const Param& param, Parser& parser, Parser::name_stack_t& name_stack, const predicate_rule_t predicate_rule, const Param* diff_param)
        {
            bool serialized = false;
            const self_t& typed_param = static_cast<const self_t&>(param);
            const self_t* diff_typed_param = static_cast<const self_t*>(diff_param);

            LLPredicate::Value<ESerializePredicates> predicate;
            if (diff_typed_param && ParamCompare<T>::equals(typed_param.getValue(), diff_typed_param->getValue()))
            {
                predicate.set(HAS_DEFAULT_VALUE);
            }

            predicate.set(VALID, typed_param.isValid());
            predicate.set(PROVIDED, typed_param.anyProvided());
            predicate.set(EMPTY, false);

            if (!predicate_rule.check(predicate)) return false;

            if (!name_stack.empty())
            {
                name_stack.back().second = true;
            }

            std::string key = typed_param.getValueName();

            // first try to write out name of name/value pair

            if (!key.empty())
            {
                if (!diff_typed_param || !ParamCompare<std::string>::equals(diff_typed_param->getValueName(), key))
                {
                    serialized = parser.writeValue(key, name_stack);
                }
            }
            // then try to serialize value directly
            else if (!diff_typed_param || ParamCompare<T>::equals(typed_param.getValue(), diff_typed_param->getValue()))
            {
                serialized = parser.writeValue(typed_param.getValue(), name_stack);
                if (!serialized)
                {
                    std::string calculated_key = typed_param.calcValueName(typed_param.getValue());
                    if (calculated_key.size()
                        && (!diff_typed_param
                            || !ParamCompare<std::string>::equals(static_cast<const self_t*>(diff_param)->getValueName(), calculated_key)))
                    {
                        serialized = parser.writeValue(calculated_key, name_stack);
                    }
                }
            }
            return serialized;
        }

        static void inspectParam(const Param& param, Parser& parser, Parser::name_stack_t& name_stack, S32 min_count, S32 max_count)
        {
            // tell parser about our actual type
            parser.inspectValue<T>(name_stack, min_count, max_count, NULL);
            // then tell it about string-based alternatives ("red", "blue", etc. for LLColor4)
            if (named_value_t::getPossibleValues())
            {
                parser.inspectValue<std::string>(name_stack, min_count, max_count, named_value_t::getPossibleValues());
            }
        }

        void set(const value_t& val, bool flag_as_provided = true)
        {
            named_value_t::clearValueName();
            named_value_t::setValue(val);
            setProvided(flag_as_provided);
        }

        self_t& operator =(const typename named_value_t::name_t& name)
        {
            named_value_t::assignNamedValue(name);
            return *this;
        }

    protected:

        self_t& operator =(const self_t& other)
        {
            param_value_t::operator =(other);
            Param::operator =(other);
            return *this;
        }

        static bool mergeWith(Param& dst, const Param& src, bool overwrite)
        {
            const self_t& src_typed_param = static_cast<const self_t&>(src);
            self_t& dst_typed_param = static_cast<self_t&>(dst);

            if (src_typed_param.isProvided()
                && (overwrite || !dst_typed_param.isProvided()))
            {
                dst_typed_param.set(src_typed_param.getValue());
                return true;
            }
            return false;
        }
    private:
        void init( BlockDescriptor &block_descriptor, ParamDescriptor::validation_func_t validate_func, S32 min_count, S32 max_count, const char* name )
        {
            ParamDescriptorPtr param_descriptor = ParamDescriptorPtr(new ParamDescriptor(
                block_descriptor.mCurrentBlockPtr->getHandleFromParam(this),
                &mergeWith,
                &deserializeParam,
                &serializeParam,
                validate_func,
                &inspectParam,
                min_count, max_count));
            block_descriptor.addParam(param_descriptor, name);
        }
    };

    // parameter that is a block
    template <typename BLOCK_T, typename NAME_VALUE_LOOKUP>
    class TypedParam<BLOCK_T, NAME_VALUE_LOOKUP, false, IS_A_BLOCK>
    :   public Param,
        public NAME_VALUE_LOOKUP::type_value_t
    {
    protected:
        typedef ParamValue<typename LLTypeTags::Sorted<BLOCK_T>::value_t>   param_value_t;
        typedef typename param_value_t::default_value_t                     default_value_t;
        typedef TypedParam<BLOCK_T, NAME_VALUE_LOOKUP, false, IS_A_BLOCK>   self_t;
        typedef typename NAME_VALUE_LOOKUP::type_value_t                    named_value_t;
    public:
        using named_value_t::operator();
        typedef typename param_value_t::value_t                             value_t;

        TypedParam(BlockDescriptor& block_descriptor, const char* name, const default_value_t& value, ParamDescriptor::validation_func_t validate_func, S32 min_count, S32 max_count)
        :   Param(block_descriptor.mCurrentBlockPtr),
            named_value_t(value)
        {
            if (LL_UNLIKELY(block_descriptor.mInitializationState == BlockDescriptor::INITIALIZING))
            {
                init(block_descriptor, validate_func, min_count, max_count, name);
            }
        }

        static bool deserializeParam(Param& param, Parser& parser, Parser::name_stack_range_t& name_stack_range, bool new_name)
        {
            self_t& typed_param = static_cast<self_t&>(param);

            if (name_stack_range.first == name_stack_range.second)
            {   // try to parse a known named value
                std::string name;

                if(named_value_t::valueNamesExist()
                    && parser.readValue(name)
                    && named_value_t::getValueFromName(name, typed_param.getValue()))
            {
                typed_param.setValueName(name);
                typed_param.setProvided();
                return true;
            }
            }

            if(typed_param.deserializeBlock(parser, name_stack_range, new_name))
            {   // attempt to parse block...
                typed_param.clearValueName();
                typed_param.setProvided();
                return true;
            }


            return false;
        }

        static bool serializeParam(const Param& param, Parser& parser, Parser::name_stack_t& name_stack, const predicate_rule_t predicate_rule, const Param* diff_param)
        {
            const self_t& typed_param = static_cast<const self_t&>(param);

            LLPredicate::Value<ESerializePredicates> predicate;

            predicate.set(VALID, typed_param.isValid());
            predicate.set(PROVIDED, typed_param.anyProvided());

            if (!predicate_rule.check(predicate)) return false;

            if (!name_stack.empty())
            {
                name_stack.back().second = true;
            }

            std::string key = typed_param.getValueName();
            if (!key.empty())
            {
                if (!diff_param || !ParamCompare<std::string>::equals(static_cast<const self_t*>(diff_param)->getValueName(), key))
                {
                    parser.writeValue(key, name_stack);
                    return true;
                }
            }
            else
            {
                return typed_param.serializeBlock(parser, name_stack, predicate_rule, static_cast<const self_t*>(diff_param));
            }

            return false;
        }

        static void inspectParam(const Param& param, Parser& parser, Parser::name_stack_t& name_stack, S32 min_count, S32 max_count)
        {
            const self_t& typed_param = static_cast<const self_t&>(param);

            // tell parser about our actual type
            parser.inspectValue<value_t>(name_stack, min_count, max_count, NULL);
            // then tell it about string-based alternatives ("red", "blue", etc. for LLColor4)
            if (named_value_t::getPossibleValues())
            {
                parser.inspectValue<std::string>(name_stack, min_count, max_count, named_value_t::getPossibleValues());
            }

            typed_param.inspectBlock(parser, name_stack, min_count, max_count);
        }

        // a param-that-is-a-block is provided when the user has set one of its child params
        // *and* the block as a whole validates
        bool isProvided() const
        {
            return Param::anyProvided() && isValid();
        }

        bool isValid() const
        {
            return param_value_t::isValid();
        }

        // assign block contents to this param-that-is-a-block
        void set(const value_t& val, bool flag_as_provided = true)
        {
            named_value_t::setValue(val);
            named_value_t::clearValueName();
            setProvided(flag_as_provided);
        }

        self_t& operator =(const typename named_value_t::name_t& name)
        {
            named_value_t::assignNamedValue(name);
            return *this;
        }

        // propagate changed status up to enclosing block
        /*virtual*/ void paramChanged(const Param& changed_param, bool user_provided)
        {
            param_value_t::paramChanged(changed_param, user_provided);

            if (user_provided)
            {
                setProvided();
                named_value_t::clearValueName();
            }
            else
            {
                Param::enclosingBlock().paramChanged(*this, user_provided);
            }
        }

    protected:

        self_t& operator =(const self_t& other)
        {
            param_value_t::operator =(other);
            Param::operator =(other);
            return *this;
        }

        static bool mergeWith(Param& dst, const Param& src, bool overwrite)
        {
            const self_t& src_typed_param = static_cast<const self_t&>(src);
            self_t& dst_typed_param = static_cast<self_t&>(dst);

            if (src_typed_param.anyProvided())
            {
                if (dst_typed_param.mergeBlockParam(src_typed_param.isProvided(), dst_typed_param.isProvided(), param_value_t::getBlockDescriptor(), src_typed_param, overwrite))
                {
                    dst_typed_param.clearValueName();
                    dst_typed_param.setProvided(true);
                    return true;
                }
            }
            return false;
        }

    private:
        void init( BlockDescriptor &block_descriptor, ParamDescriptor::validation_func_t validate_func, S32 min_count, S32 max_count, const char* name )
        {
            ParamDescriptorPtr param_descriptor = ParamDescriptorPtr(new ParamDescriptor(
                block_descriptor.mCurrentBlockPtr->getHandleFromParam(this),
                &mergeWith,
                &deserializeParam,
                &serializeParam,
                validate_func,
                &inspectParam,
                min_count, max_count));
            block_descriptor.addParam(param_descriptor, name);
        }
    };

    // list of non-block parameters
    template <typename MULTI_VALUE_T, typename NAME_VALUE_LOOKUP>
    class TypedParam<MULTI_VALUE_T, NAME_VALUE_LOOKUP, true, NOT_BLOCK>
    :   public Param
    {
    protected:
        typedef TypedParam<MULTI_VALUE_T, NAME_VALUE_LOOKUP, true, NOT_BLOCK>       self_t;
        typedef ParamValue<typename LLTypeTags::Sorted<MULTI_VALUE_T>::value_t> param_value_t;
        typedef typename std::vector<typename NAME_VALUE_LOOKUP::type_value_t>  container_t;
        typedef container_t                                                     default_value_t;
        typedef typename NAME_VALUE_LOOKUP::type_value_t                        named_value_t;

    public:
        typedef typename param_value_t::value_t                             value_t;

        TypedParam(BlockDescriptor& block_descriptor, const char* name, const default_value_t& value, ParamDescriptor::validation_func_t validate_func, S32 min_count, S32 max_count)
        :   Param(block_descriptor.mCurrentBlockPtr),
            mMinCount(min_count),
            mMaxCount(max_count)
        {
            std::copy(value.begin(), value.end(), std::back_inserter(mValues));

            if (LL_UNLIKELY(block_descriptor.mInitializationState == BlockDescriptor::INITIALIZING))
            {
                init(block_descriptor, validate_func, min_count, max_count, name);

            }
        }

        bool isProvided() const { return Param::anyProvided() && isValid(); }

        bool isValid() const
        {
            size_t num_elements = numValidElements();
            return mMinCount < num_elements && num_elements < mMaxCount;
        }

        static bool deserializeParam(Param& param, Parser& parser, Parser::name_stack_range_t& name_stack_range, bool new_name)
        {
            Parser::name_stack_range_t new_name_stack_range(name_stack_range);
            self_t& typed_param = static_cast<self_t&>(param);
            value_t value;

            // pop first element if empty string
            if (new_name_stack_range.first != new_name_stack_range.second && new_name_stack_range.first->first.empty())
            {
                ++new_name_stack_range.first;
            }

            // no further names in stack, attempt to parse value now
            if (new_name_stack_range.first == new_name_stack_range.second)
            {
                std::string name;

                // try to parse a known named value
                if(named_value_t::valueNamesExist()
                    && parser.readValue(name)
                    && named_value_t::getValueFromName(name, value))
                {
                    typed_param.add(value);
                    typed_param.mValues.back().setValueName(name);
                    return true;
                }
                else if (parser.readValue(value))   // attempt to read value directly
                {
                    typed_param.add(value);
                    return true;
                }
            }
            return false;
        }

        static bool serializeParam(const Param& param, Parser& parser, Parser::name_stack_t& name_stack, const predicate_rule_t predicate_rule, const Param* diff_param)
        {
            bool serialized = false;
            const self_t& typed_param = static_cast<const self_t&>(param);

            LLPredicate::Value<ESerializePredicates> predicate;

            predicate.set(REQUIRED, typed_param.mMinCount > 0);
            predicate.set(VALID, typed_param.isValid());
            predicate.set(PROVIDED, typed_param.anyProvided());
            predicate.set(EMPTY, typed_param.mValues.empty());

            if (!predicate_rule.check(predicate)) return false;

            for (const_iterator it = typed_param.mValues.begin(), end_it = typed_param.mValues.end();
                it != end_it;
                ++it)
            {
                std::string key = it->getValueName();
                name_stack.push_back(std::make_pair(std::string(), true));

                if(key.empty())
                // not parsed via name values, write out value directly
                {
                    bool value_written = parser.writeValue(*it, name_stack);
                    if (!value_written)
                    {
                        std::string calculated_key = it->calcValueName(it->getValue());
                        if (parser.writeValue(calculated_key, name_stack))
                        {
                            serialized = true;
                        }
                        else
                        {
                            break;
                        }
                    }
                }
                else
                {
                    if(parser.writeValue(key, name_stack))
                    {
                        serialized = true;
                    }
                    else
                    {
                        break;
                    }
                }
            }

            return serialized;
        }

        static void inspectParam(const Param& param, Parser& parser, Parser::name_stack_t& name_stack, S32 min_count, S32 max_count)
        {
            parser.inspectValue<MULTI_VALUE_T>(name_stack, min_count, max_count, NULL);
            if (named_value_t::getPossibleValues())
            {
                parser.inspectValue<std::string>(name_stack, min_count, max_count, named_value_t::getPossibleValues());
            }
        }

        void set(const container_t& val, bool flag_as_provided = true)
        {
            mValues = val;
            setProvided(flag_as_provided);
        }

        param_value_t& add()
        {
            mValues.push_back(value_t());
            Param::setProvided();
            return mValues.back();
        }

        self_t& add(const value_t& item)
        {
            mValues.push_back(item);
            setProvided();
            return *this;
        }

        self_t& add(const typename named_value_t::name_t& name)
        {
            value_t value;

            // try to parse a per type named value
            if (named_value_t::getValueFromName(name, value))
            {
                add(value);
                mValues.back().setValueName(name);
            }

            return *this;
        }

        // implicit conversion
        operator const container_t&() const { return mValues; }
        // explicit conversion
        const container_t& operator()() const { return mValues; }

        typedef typename container_t::iterator iterator;
        typedef typename container_t::const_iterator const_iterator;
        iterator begin() { return mValues.begin(); }
        iterator end() { return mValues.end(); }
        const_iterator begin() const { return mValues.begin(); }
        const_iterator end() const { return mValues.end(); }
        bool empty() const { return mValues.empty(); }
        size_t size() const { return mValues.size(); }

        size_t numValidElements() const
        {
            return mValues.size();
        }

    protected:
        static bool mergeWith(Param& dst, const Param& src, bool overwrite)
        {
            const self_t& src_typed_param = static_cast<const self_t&>(src);
            self_t& dst_typed_param = static_cast<self_t&>(dst);

            if (overwrite)
            {
                std::copy(src_typed_param.begin(), src_typed_param.end(), std::back_inserter(dst_typed_param.mValues));
            }
            else
            {
                container_t new_values(src_typed_param.mValues);
                std::copy(dst_typed_param.begin(), dst_typed_param.end(), std::back_inserter(new_values));
                std::swap(dst_typed_param.mValues, new_values);
            }

            if (src_typed_param.begin() != src_typed_param.end())
            {
                dst_typed_param.setProvided();
            }
            return true;
        }

        container_t     mValues;
        size_t          mMinCount,
                        mMaxCount;

    private:
        void init( BlockDescriptor &block_descriptor, ParamDescriptor::validation_func_t validate_func, S32 min_count, S32 max_count, const char* name )
        {
            ParamDescriptorPtr param_descriptor = ParamDescriptorPtr(new ParamDescriptor(
                block_descriptor.mCurrentBlockPtr->getHandleFromParam(this),
                &mergeWith,
                &deserializeParam,
                &serializeParam,
                validate_func,
                &inspectParam,
                min_count, max_count));
            block_descriptor.addParam(param_descriptor, name);
        }
    };

    // list of block parameters
    template <typename MULTI_BLOCK_T, typename NAME_VALUE_LOOKUP>
    class TypedParam<MULTI_BLOCK_T, NAME_VALUE_LOOKUP, true, IS_A_BLOCK>
    :   public Param
    {
    protected:
        typedef TypedParam<MULTI_BLOCK_T, NAME_VALUE_LOOKUP, true, IS_A_BLOCK>      self_t;
        typedef ParamValue<typename LLTypeTags::Sorted<MULTI_BLOCK_T>::value_t> param_value_t;
        typedef typename std::vector<typename NAME_VALUE_LOOKUP::type_value_t>  container_t;
        typedef typename NAME_VALUE_LOOKUP::type_value_t                        named_value_t;
        typedef container_t                                                     default_value_t;
        typedef typename container_t::iterator                                  iterator;
        typedef typename container_t::const_iterator                            const_iterator;
    public:
        typedef typename param_value_t::value_t                         value_t;

        TypedParam(BlockDescriptor& block_descriptor, const char* name, const default_value_t& value, ParamDescriptor::validation_func_t validate_func, S32 min_count, S32 max_count)
        :   Param(block_descriptor.mCurrentBlockPtr),
            mMinCount(min_count),
            mMaxCount(max_count)
        {
            std::copy(value.begin(), value.end(), back_inserter(mValues));

            if (LL_UNLIKELY(block_descriptor.mInitializationState == BlockDescriptor::INITIALIZING))
            {
                init(block_descriptor, validate_func, min_count, max_count, name);
            }
        }

        bool isProvided() const { return Param::anyProvided() && isValid(); }

        bool isValid() const
        {
            size_t num_elements = numValidElements();
            return mMinCount < num_elements && num_elements < mMaxCount;
        }


        static bool deserializeParam(Param& param, Parser& parser, Parser::name_stack_range_t& name_stack_range, bool new_name)
        {
            Parser::name_stack_range_t new_name_stack_range(name_stack_range);
            self_t& typed_param = static_cast<self_t&>(param);
            bool new_value = false;
            bool new_array_value = false;

            // pop first element if empty string
            if (new_name_stack_range.first != new_name_stack_range.second && new_name_stack_range.first->first.empty())
            {
                new_array_value = new_name_stack_range.first->second;
                ++new_name_stack_range.first;
            }

            if (new_name || new_array_value || typed_param.mValues.empty())
            {
                new_value = true;
                typed_param.mValues.push_back(value_t());
            }
            param_value_t& value = typed_param.mValues.back();

            if (new_name_stack_range.first == new_name_stack_range.second)
            {   // try to parse a known named value
                std::string name;

                if(named_value_t::valueNamesExist()
                    && parser.readValue(name)
                    && named_value_t::getValueFromName(name, value.getValue()))
                {
                    typed_param.mValues.back().setValueName(name);
                    typed_param.setProvided();
                    if (new_array_value)
                    {
                        name_stack_range.first->second = false;
                    }
                    return true;
                }
            }

            // attempt to parse block...
            if(value.deserializeBlock(parser, new_name_stack_range, new_name))
            {
                typed_param.setProvided();
                if (new_array_value)
                {
                    name_stack_range.first->second = false;
                }
                return true;
            }


            if (new_value)
            {   // failed to parse new value, pop it off
                typed_param.mValues.pop_back();
            }

            return false;
        }

        static bool serializeParam(const Param& param, Parser& parser, Parser::name_stack_t& name_stack, const predicate_rule_t predicate_rule, const Param* diff_param)
        {
            bool serialized = false;
            const self_t& typed_param = static_cast<const self_t&>(param);
            LLPredicate::Value<ESerializePredicates> predicate;

            predicate.set(REQUIRED, typed_param.mMinCount > 0);
            predicate.set(VALID, typed_param.isValid());
            predicate.set(PROVIDED, typed_param.anyProvided());
            predicate.set(EMPTY, typed_param.mValues.empty());

            if (!predicate_rule.check(predicate)) return false;

            for (const_iterator it = typed_param.mValues.begin(), end_it = typed_param.mValues.end();
                it != end_it;
                ++it)
            {
                name_stack.push_back(std::make_pair(std::string(), true));

                std::string key = it->getValueName();
                if (!key.empty())
                {
                    serialized |= parser.writeValue(key, name_stack);
                }
                // Not parsed via named values, write out value directly
                // NOTE: currently we don't do diffing of Multiples
                else
                {
                    serialized = it->serializeBlock(parser, name_stack, predicate_rule, NULL);
                }

                name_stack.pop_back();
            }

            if (!serialized && predicate_rule.check(ll_make_predicate(EMPTY)))
            {
                serialized |= parser.writeValue(Flag(), name_stack);
            }

            return serialized;
        }

        static void inspectParam(const Param& param, Parser& parser, Parser::name_stack_t& name_stack, S32 min_count, S32 max_count)
        {
            const param_value_t& value_param = param_value_t(value_t());

            // tell parser about our actual type
            parser.inspectValue<value_t>(name_stack, min_count, max_count, NULL);
            // then tell it about string-based alternatives ("red", "blue", etc. for LLColor4)
            if (named_value_t::getPossibleValues())
            {
                parser.inspectValue<std::string>(name_stack, min_count, max_count, named_value_t::getPossibleValues());
        }

            value_param.inspectBlock(parser, name_stack, min_count, max_count);
        }

        void set(const container_t& val, bool flag_as_provided = true)
        {
            mValues = val;
            setProvided(flag_as_provided);
        }

        param_value_t& add()
        {
            mValues.push_back(value_t());
            setProvided();
            return mValues.back();
        }

        self_t& add(const value_t& item)
        {
            mValues.push_back(item);
            setProvided();
            return *this;
        }

        self_t& add(const typename named_value_t::name_t& name)
        {
            value_t value;

            // try to parse a per type named value
            if (named_value_t::getValueFromName(name, value))
            {
                add(value);
                mValues.back().setValueName(name);
            }
            return *this;
        }

        // implicit conversion
        operator const container_t&() const { return mValues; }
        operator container_t&() { return mValues; }
        // explicit conversion
        const container_t& operator()() const { return mValues; }
        container_t& operator()() { return mValues; }
        // direct Nth item access
        const typename NAME_VALUE_LOOKUP::type_value_t& operator()(size_t index) const { return mValues[index]; }
        typename NAME_VALUE_LOOKUP::type_value_t& operator()(size_t index) { return mValues[index]; }

        iterator begin() { return mValues.begin(); }
        iterator end() { return mValues.end(); }
        const_iterator begin() const { return mValues.begin(); }
        const_iterator end() const { return mValues.end(); }
        bool empty() const { return mValues.empty(); }
        size_t size() const { return mValues.size(); }

        size_t numValidElements() const
        {
            size_t count = 0;
            for (const_iterator it = mValues.begin(), end_it = mValues.end();
                it != end_it;
                ++it)
            {
                if(it->isValid()) count++;
            }
            return count;
        }

    protected:

        static bool mergeWith(Param& dst, const Param& src, bool overwrite)
        {
            const self_t& src_typed_param = static_cast<const self_t&>(src);
            self_t& dst_typed_param = static_cast<self_t&>(dst);

            if (overwrite)
            {
                std::copy(src_typed_param.begin(), src_typed_param.end(), std::back_inserter(dst_typed_param.mValues));
            }
            else
            {
                container_t new_values(src_typed_param.mValues);
                std::copy(dst_typed_param.begin(), dst_typed_param.end(), std::back_inserter(new_values));
                std::swap(dst_typed_param.mValues, new_values);
            }

            if (src_typed_param.begin() != src_typed_param.end())
            {
                dst_typed_param.setProvided();
            }

            return true;
        }

        container_t         mValues;
        size_t              mMinCount,
                            mMaxCount;

    private:
        void init( BlockDescriptor &block_descriptor, ParamDescriptor::validation_func_t validate_func, S32 min_count, S32 max_count, const char* name )
        {
            ParamDescriptorPtr param_descriptor = ParamDescriptorPtr(new ParamDescriptor(
                block_descriptor.mCurrentBlockPtr->getHandleFromParam(this),
                &mergeWith,
                &deserializeParam,
                &serializeParam,
                validate_func,
                &inspectParam,
                min_count, max_count));
            block_descriptor.addParam(param_descriptor, name);
        }
    };

    template <typename DERIVED_BLOCK, typename BASE_BLOCK = BaseBlock>
    class ChoiceBlock : public BASE_BLOCK
    {
        typedef ChoiceBlock<DERIVED_BLOCK, BASE_BLOCK>  self_t;
        typedef ChoiceBlock<DERIVED_BLOCK, BASE_BLOCK>  enclosing_block_t;
        typedef BASE_BLOCK                              base_block_t;

        LOG_CLASS(self_t);
    public:
        // take all provided params from other and apply to self
        bool overwriteFrom(const self_t& other)
        {
            return static_cast<DERIVED_BLOCK*>(this)->mergeBlock(getBlockDescriptor(), other, true);
        }

        // take all provided params that are not already provided, and apply to self
        bool fillFrom(const self_t& other)
        {
            return static_cast<DERIVED_BLOCK*>(this)->mergeBlock(getBlockDescriptor(), other, false);
        }

        bool mergeBlockParam(bool source_provided, bool dest_provided, BlockDescriptor& block_data, const self_t& source, bool overwrite)
        {
            bool source_override = source_provided && (overwrite || !dest_provided);

            if (source_override || source.mCurChoice == mCurChoice)
            {
                return mergeBlock(block_data, source, overwrite);
            }
            return false;
        }

        // merge with other block
        bool mergeBlock(BlockDescriptor& block_data, const self_t& other, bool overwrite)
        {
            mCurChoice = other.mCurChoice;
            return base_block_t::mergeBlock(getBlockDescriptor(), other, overwrite);
        }

        // clear out old choice when param has changed
        /*virtual*/ void paramChanged(const Param& changed_param, bool user_provided)
        {
            param_handle_t changed_param_handle = base_block_t::getHandleFromParam(&changed_param);
            // if we have a new choice...
            if (changed_param_handle != mCurChoice)
            {
                // clear provided flag on previous choice
                Param* previous_choice = base_block_t::getParamFromHandle(mCurChoice);
                if (previous_choice)
                {
                    previous_choice->setProvided(false);
                }
                mCurChoice = changed_param_handle;
            }
            base_block_t::paramChanged(changed_param, user_provided);
        }

        virtual const BlockDescriptor& mostDerivedBlockDescriptor() const { return getBlockDescriptor(); }
        virtual BlockDescriptor& mostDerivedBlockDescriptor() { return getBlockDescriptor(); }

    protected:
        ChoiceBlock()
        :   mCurChoice(0)
        {
            BaseBlock::init(getBlockDescriptor(), base_block_t::getBlockDescriptor(), sizeof(DERIVED_BLOCK));
        }

        // Alternatives are mutually exclusive wrt other Alternatives in the same block.
        // One alternative in a block will always have isChosen() == true.
        // At most one alternative in a block will have isProvided() == true.
        template <typename T, typename NAME_VALUE_LOOKUP = typename TypeValues<T>::type_value_t >
        class Alternative : public TypedParam<T, NAME_VALUE_LOOKUP, false>
        {
            typedef TypedParam<T, NAME_VALUE_LOOKUP, false> super_t;
            typedef typename super_t::value_t               value_t;
            typedef typename super_t::default_value_t       default_value_t;

        public:
            friend class ChoiceBlock<DERIVED_BLOCK>;

            using super_t::operator =;

            explicit Alternative(const char* name = "", const default_value_t& val = defaultValue<default_value_t>())
            :   super_t(DERIVED_BLOCK::getBlockDescriptor(), name, val, NULL, 0, 1),
                mOriginalValue(val)
            {
                // assign initial choice to first declared option
                DERIVED_BLOCK* blockp = ((DERIVED_BLOCK*)DERIVED_BLOCK::getBlockDescriptor().mCurrentBlockPtr);
                if (LL_UNLIKELY(DERIVED_BLOCK::getBlockDescriptor().mInitializationState == BlockDescriptor::INITIALIZING))
                {
                    if(blockp->mCurChoice == 0)
                    {
                        blockp->mCurChoice = Param::enclosingBlock().getHandleFromParam(this);
                    }
                }
            }

            void choose()
            {
                static_cast<enclosing_block_t&>(Param::enclosingBlock()).paramChanged(*this, true);
            }

            void chooseAs(const value_t& val)
            {
                super_t::set(val);
            }

            void operator =(const value_t& val)
            {
                super_t::set(val);
            }

            void operator()(const value_t& val)
            {
                super_t::set(val);
            }

            operator const value_t&() const
            {
                return (*this)();
            }

            const value_t& operator()() const
            {
                if (static_cast<enclosing_block_t&>(Param::enclosingBlock()).getCurrentChoice() == this)
                {
                    return super_t::getValue();
                }
                return mOriginalValue;
            }

            bool isChosen() const
            {
                return static_cast<enclosing_block_t&>(Param::enclosingBlock()).getCurrentChoice() == this;
            }

        private:
            default_value_t mOriginalValue;
        };

    public:
        static BlockDescriptor& getBlockDescriptor()
        {
            static BlockDescriptor sBlockDescriptor;
            return sBlockDescriptor;
        }

    private:
        param_handle_t  mCurChoice;

        const Param* getCurrentChoice() const
        {
            return base_block_t::getParamFromHandle(mCurChoice);
        }
    };

    template <typename DERIVED_BLOCK, typename BASE_BLOCK = BaseBlock>
    class Block
    :   public BASE_BLOCK
    {
        typedef Block<DERIVED_BLOCK, BASE_BLOCK>    self_t;

    protected:
        typedef Block<DERIVED_BLOCK, BASE_BLOCK>    block_t;

    public:
        typedef BASE_BLOCK base_block_t;

        // take all provided params from other and apply to self
        bool overwriteFrom(const self_t& other)
        {
            return static_cast<DERIVED_BLOCK*>(this)->mergeBlock(getBlockDescriptor(), other, true);
        }

        // take all provided params that are not already provided, and apply to self
        bool fillFrom(const self_t& other)
        {
            return static_cast<DERIVED_BLOCK*>(this)->mergeBlock(getBlockDescriptor(), other, false);
        }

        virtual const BlockDescriptor& mostDerivedBlockDescriptor() const { return getBlockDescriptor(); }
        virtual BlockDescriptor& mostDerivedBlockDescriptor() { return getBlockDescriptor(); }

    protected:
        Block()
        {
            //#pragma message("Parsing LLInitParam::Block")
            BaseBlock::init(getBlockDescriptor(), BASE_BLOCK::getBlockDescriptor(), sizeof(DERIVED_BLOCK));
        }

        //
        // Nested classes for declaring parameters
        //
        template <typename T, typename NAME_VALUE_LOOKUP = typename TypeValues<T>::type_value_t >
        class Optional : public TypedParam<T, NAME_VALUE_LOOKUP, false>
        {
            typedef TypedParam<T, NAME_VALUE_LOOKUP, false>     super_t;
            typedef typename super_t::value_t                   value_t;
            typedef typename super_t::default_value_t           default_value_t;

        public:
            using super_t::operator();
            using super_t::operator =;

            explicit Optional(const char* name = "", const default_value_t& val = defaultValue<default_value_t>())
            :   super_t(DERIVED_BLOCK::getBlockDescriptor(), name, val, NULL, 0, 1)
            {
                //#pragma message("Parsing LLInitParam::Block::Optional")
            }

            Optional& operator =(const value_t& val)
            {
                super_t::set(val);
                return *this;
            }

            DERIVED_BLOCK& operator()(const value_t& val)
            {
                super_t::set(val);
                return static_cast<DERIVED_BLOCK&>(Param::enclosingBlock());
            }
        };

        template <typename T, typename NAME_VALUE_LOOKUP = typename TypeValues<T>::type_value_t >
        class Mandatory : public TypedParam<T, NAME_VALUE_LOOKUP, false>
        {
            typedef TypedParam<T, NAME_VALUE_LOOKUP, false>     super_t;
            typedef Mandatory<T, NAME_VALUE_LOOKUP>             self_t;
            typedef typename super_t::value_t                   value_t;
            typedef typename super_t::default_value_t           default_value_t;

        public:
            using super_t::operator();
            using super_t::operator =;

            // mandatory parameters require a name to be parseable
            explicit Mandatory(const char* name = "", const default_value_t& val = defaultValue<default_value_t>())
            :   super_t(DERIVED_BLOCK::getBlockDescriptor(), name, val, &validate, 1, 1)
            {}

            Mandatory& operator =(const value_t& val)
            {
                super_t::set(val);
                return *this;
            }

            DERIVED_BLOCK& operator()(const value_t& val)
            {
                super_t::set(val);
                return static_cast<DERIVED_BLOCK&>(Param::enclosingBlock());
            }

            static bool validate(const Param* p)
            {
                // valid only if provided
                return static_cast<const self_t*>(p)->isProvided();
            }

        };

        template <typename T, typename RANGE = BaseBlock::AnyAmount, typename NAME_VALUE_LOOKUP = typename TypeValues<T>::type_value_t >
        class Multiple : public TypedParam<T, NAME_VALUE_LOOKUP, true>
        {
            typedef TypedParam<T, NAME_VALUE_LOOKUP, true>  super_t;
            typedef Multiple<T, RANGE, NAME_VALUE_LOOKUP>   self_t;
            typedef typename super_t::container_t           container_t;
            typedef typename super_t::value_t               value_t;

        public:
            typedef typename super_t::iterator              iterator;
            typedef typename super_t::const_iterator        const_iterator;

            using super_t::operator();
            using super_t::operator const container_t&;

            explicit Multiple(const char* name = "")
            :   super_t(DERIVED_BLOCK::getBlockDescriptor(), name, container_t(), &validate, RANGE::minCount, RANGE::maxCount)
            {}

            Multiple& operator =(const container_t& val)
            {
                super_t::set(val);
                return *this;
            }

            DERIVED_BLOCK& operator()(const container_t& val)
            {
                super_t::set(val);
                return static_cast<DERIVED_BLOCK&>(Param::enclosingBlock());
            }

            static bool validate(const Param* paramp)
            {
                size_t num_valid = ((super_t*)paramp)->numValidElements();
                return RANGE::minCount <= num_valid && num_valid <= RANGE::maxCount;
            }
        };

        // can appear in data files, but will ignored during parsing
        // cannot read or write in code
        class Ignored : public Param
        {
        public:
            explicit Ignored(const char* name)
            :   Param(DERIVED_BLOCK::getBlockDescriptor().mCurrentBlockPtr)
            {
                BlockDescriptor& block_descriptor = DERIVED_BLOCK::getBlockDescriptor();
                if (LL_UNLIKELY(block_descriptor.mInitializationState == BlockDescriptor::INITIALIZING))
                {
                    ParamDescriptorPtr param_descriptor = ParamDescriptorPtr(new ParamDescriptor(
                                                    block_descriptor.mCurrentBlockPtr->getHandleFromParam(this),
                                                    NULL,
                                                    &deserializeParam,
                                                    NULL,
                                                    NULL,
                                                    NULL,
                                                    0, S32_MAX));
                    block_descriptor.addParam(param_descriptor, name);
                }
            }

            static bool deserializeParam(Param& param, Parser& parser, Parser::name_stack_range_t& name_stack_range, bool new_name)
            {
                if (name_stack_range.first == name_stack_range.second)
                {
                    //std::string message = llformat("Deprecated value %s ignored", getName().c_str());
                    //parser.parserWarning(message);
                    return true;
                }

                return false;
            }
        };

        // can appear in data files, or be written to in code, but data will be ignored
        // cannot be read in code
        class Deprecated : public Ignored
        {
        public:
            explicit Deprecated(const char* name) : Ignored(name) {}

            // dummy writer interfaces
            template<typename T>
            Deprecated& operator =(const T& val)
        {
                // do nothing
                return *this;
            }

            template<typename T>
            DERIVED_BLOCK& operator()(const T& val)
            {
                // do nothing
                return static_cast<DERIVED_BLOCK&>(Param::enclosingBlock());
            }

            template<typename T>
            void set(const T& val, bool flag_as_provided = true)
            {
                // do nothing
            }
        };

    public:
        static BlockDescriptor& getBlockDescriptor()
        {
            static BlockDescriptor sBlockDescriptor;
            return sBlockDescriptor;
        }

    protected:
        template <typename T, typename NAME_VALUE_LOOKUP, bool multiple, typename is_block>
        void changeDefault(TypedParam<T, NAME_VALUE_LOOKUP, multiple, is_block>& param,
            const typename TypedParam<T, NAME_VALUE_LOOKUP, multiple, is_block>::value_t& value)
        {
            if (!param.isProvided())
            {
                param.set(value, false);
            }
        }

    };

    template<typename T, typename BLOCK_T>
    struct IsBlock<ParamValue<BaseBlock::Lazy<T, BaseBlock::IS_A_BLOCK>, BLOCK_T >, void>
    {
        typedef IS_A_BLOCK value_t;
    };

    template<typename T, typename BLOCK_T>
    struct IsBlock<ParamValue<BaseBlock::Lazy<T, BaseBlock::NOT_A_BLOCK>, BLOCK_T >, void>
    {
        typedef NOT_BLOCK value_t;
    };

    template<typename T, typename BLOCK_IDENTIFIER>
    struct IsBlock<ParamValue<BaseBlock::Atomic<T>, typename IsBlock<BaseBlock::Atomic<T> >::value_t >, BLOCK_IDENTIFIER>
    {
        typedef typename IsBlock<T>::value_t value_t;
    };

    template<typename T, typename BLOCK_IDENTIFIER>
    struct IsBlock<ParamValue<BaseBlock::Sequential<T>, typename IsBlock<BaseBlock::Sequential<T> >::value_t >, BLOCK_IDENTIFIER>
    {
        typedef typename IsBlock<T>::value_t value_t;
    };


    template<typename T>
    struct InnerMostType
    {
        typedef T value_t;
    };

    template<typename T>
    struct InnerMostType<ParamValue<T, NOT_BLOCK> >
    {
        typedef typename InnerMostType<T>::value_t value_t;
    };

    template<typename T>
    struct InnerMostType<ParamValue<T, IS_A_BLOCK> >
    {
        typedef typename InnerMostType<T>::value_t value_t;
    };

    template<typename T, typename BLOCK_T>
    class ParamValue <BaseBlock::Atomic<T>, BLOCK_T>
    {
        typedef ParamValue <BaseBlock::Atomic<T>, BLOCK_T> self_t;

    public:
        typedef typename InnerMostType<T>::value_t  value_t;
        typedef T                                   default_value_t;

        ParamValue()
        :   mValue()
        {}

        ParamValue(const default_value_t& value)
        :   mValue(value)
        {}

        void setValue(const value_t& val)
        {
            mValue.setValue(val);
        }

        const value_t& getValue() const
        {
            return mValue.getValue();
        }

        value_t& getValue()
        {
            return mValue.getValue();
        }

        bool deserializeBlock(Parser& p, Parser::name_stack_range_t& name_stack_range, bool new_name)
        {
            if (new_name)
            {
                resetToDefault();
            }
            return mValue.deserializeBlock(p, name_stack_range, new_name);
        }

        bool serializeBlock(Parser& p, Parser::name_stack_t& name_stack, const predicate_rule_t predicate_rule, const self_t* diff_block = NULL) const
        {
            const BaseBlock* base_block = diff_block
                ? &(diff_block->mValue)
                : NULL;
            return mValue.serializeBlock(p, name_stack, predicate_rule, base_block);
        }

        bool inspectBlock(Parser& p, Parser::name_stack_t name_stack = Parser::name_stack_t(), S32 min_count = 0, S32 max_count = S32_MAX) const
        {
            return mValue.inspectBlock(p, name_stack, min_count, max_count);
        }

        bool mergeBlockParam(bool source_provided, bool dst_provided, BlockDescriptor& block_data, const self_t& source, bool overwrite)
        {
            if ((overwrite && source_provided) // new values coming in on top or...
                || (!overwrite && !dst_provided)) // values being pushed under with nothing already there
            {
                // clear away what is there and take the new stuff as a whole
                resetToDefault();
                return mValue.mergeBlock(block_data, source.getValue(), overwrite);
            }
            return mValue.mergeBlock(block_data, source.getValue(), overwrite);
        }

        bool validateBlock(bool emit_errors = true) const
        {
            return mValue.validateBlock(emit_errors);
        }

        bool isValid() const
        {
            return validateBlock(false);
        }

        static BlockDescriptor& getBlockDescriptor()
        {
            return value_t::getBlockDescriptor();
        }


    private:
        void resetToDefault()
        {
            static T default_value;
            mValue = default_value;
        }

        T   mValue;
    };

    template<typename T>
    class ParamValue <BaseBlock::Sequential<T>, IS_A_BLOCK>
    {
        typedef ParamValue <BaseBlock::Sequential<T>, IS_A_BLOCK> self_t;

    public:
        typedef typename InnerMostType<T>::value_t  value_t;
        typedef T                                   default_value_t;

        ParamValue()
        :   mValue()
        {
            mCurParam = getBlockDescriptor().mAllParams.begin();
        }

        ParamValue(const default_value_t& value)
        :   mValue(value)
        {
            mCurParam = getBlockDescriptor().mAllParams.begin();
        }

        void setValue(const value_t& val)
        {
            mValue.setValue(val);
        }

        const value_t& getValue() const
        {
            return mValue.getValue();
        }

        value_t& getValue()
        {
            return mValue.getValue();
        }

        bool deserializeBlock(Parser& p, Parser::name_stack_range_t& name_stack_range, bool new_name)
        {
            if (new_name)
            {
                mCurParam = getBlockDescriptor().mAllParams.begin();
            }
            if (name_stack_range.first == name_stack_range.second
                && mCurParam != getBlockDescriptor().mAllParams.end())
            {
                // deserialize to mCurParam
                ParamDescriptor& pd = *(*mCurParam);
                ParamDescriptor::deserialize_func_t deserialize_func = pd.mDeserializeFunc;
                Param* paramp = mValue.getParamFromHandle(pd.mParamHandle);

                if (deserialize_func
                    && paramp
                    && deserialize_func(*paramp, p, name_stack_range, new_name))
                {
                    ++mCurParam;
                    return true;
                }
                else
                {
                    return false;
                }
            }
            else
            {
                return mValue.deserializeBlock(p, name_stack_range, new_name);
            }
        }

        bool serializeBlock(Parser& p, Parser::name_stack_t& name_stack, const predicate_rule_t predicate_rule, const self_t* diff_block = NULL) const
        {
            const BaseBlock* base_block = diff_block
                ? &(diff_block->mValue)
                : NULL;
            return mValue.serializeBlock(p, name_stack, predicate_rule, base_block);
        }

        bool inspectBlock(Parser& p, Parser::name_stack_t name_stack = Parser::name_stack_t(), S32 min_count = 0, S32 max_count = S32_MAX) const
        {
            return mValue.inspectBlock(p, name_stack, min_count, max_count);
        }

        bool mergeBlockParam(bool source_provided, bool dst_provided, BlockDescriptor& block_data, const self_t& source, bool overwrite)
        {
            return mValue.mergeBlock(block_data, source.getValue(), overwrite);
        }

        bool validateBlock(bool emit_errors = true) const
        {
            return mValue.validateBlock(emit_errors);
        }

        bool isValid() const
        {
            return validateBlock(false);
        }

        static BlockDescriptor& getBlockDescriptor()
        {
            return value_t::getBlockDescriptor();
        }

    private:

        BlockDescriptor::all_params_list_t::iterator    mCurParam;
        T                                               mValue;
    };

    template<typename T>
    class ParamValue <BaseBlock::Sequential<T>, NOT_BLOCK>
    : public T
    {
        typedef ParamValue <BaseBlock::Sequential<T>, NOT_BLOCK> self_t;

    public:
        typedef typename InnerMostType<T>::value_t  value_t;
        typedef T                                   default_value_t;

        ParamValue()
        :   T()
        {}

        ParamValue(const default_value_t& value)
        :   T(value.getValue())
        {}

        bool isValid() const { return true; }
    };

    template<typename T, typename BLOCK_T>
    class ParamValue <BaseBlock::Lazy<T, IS_A_BLOCK>, BLOCK_T>
    {
        typedef ParamValue <BaseBlock::Lazy<T, IS_A_BLOCK>, BLOCK_T> self_t;

    public:
        typedef typename InnerMostType<T>::value_t  value_t;
        typedef LazyValue<T>                        default_value_t;

        ParamValue()
        :   mValue()
        {}

        ParamValue(const default_value_t& other)
        :   mValue(other)
        {}

        ParamValue(const T& value)
        :   mValue(value)
        {}

        void setValue(const value_t& val)
        {
            mValue.set(val);
        }

        const value_t& getValue() const
        {
            return mValue.get().getValue();
        }

        value_t& getValue()
        {
            return mValue.get().getValue();
        }

        bool deserializeBlock(Parser& p, Parser::name_stack_range_t& name_stack_range, bool new_name)
        {
            return mValue.get().deserializeBlock(p, name_stack_range, new_name);
        }

        bool serializeBlock(Parser& p, Parser::name_stack_t& name_stack, const predicate_rule_t predicate_rule, const self_t* diff_block = NULL) const
        {
            if (mValue.empty()) return false;

            const BaseBlock* base_block = (diff_block && !diff_block->mValue.empty())
                                            ? &(diff_block->mValue.get().getValue())
                                            : NULL;
            return mValue.get().serializeBlock(p, name_stack, predicate_rule, base_block);
        }

        bool inspectBlock(Parser& p, Parser::name_stack_t name_stack = Parser::name_stack_t(), S32 min_count = 0, S32 max_count = S32_MAX) const
        {
            return mValue.get().inspectBlock(p, name_stack, min_count, max_count);
        }

        bool mergeBlockParam(bool source_provided, bool dst_provided, BlockDescriptor& block_data, const self_t& source, bool overwrite)
        {
            return source.mValue.empty() || mValue.get().mergeBlock(block_data, source.getValue(), overwrite);
        }

        bool validateBlock(bool emit_errors = true) const
        {
            return mValue.empty() || mValue.get().validateBlock(emit_errors);
        }

        bool isValid() const
        {
            return validateBlock(false);
        }

        static BlockDescriptor& getBlockDescriptor()
        {
            return value_t::getBlockDescriptor();
        }

    private:
        LazyValue<T>    mValue;
    };

    template<typename T, typename BLOCK_T>
    class ParamValue <BaseBlock::Lazy<T, NOT_BLOCK>, BLOCK_T>
    {
        typedef ParamValue <BaseBlock::Lazy<T, NOT_BLOCK>, BLOCK_T> self_t;

    public:
        typedef typename InnerMostType<T>::value_t  value_t;
        typedef LazyValue<T>                        default_value_t;

        ParamValue()
        :   mValue()
        {}

        ParamValue(const default_value_t& other)
        :   mValue(other)
        {}

        ParamValue(const T& value)
        :   mValue(value)
        {}

        void setValue(const value_t& val)
        {
            mValue.set(val);
        }

        const value_t& getValue() const
        {
            return mValue.get().getValue();
        }

        value_t& getValue()
        {
            return mValue.get().getValue();
        }

        bool isValid() const
        {
            return true;
        }

    private:
        LazyValue<T>    mValue;
    };

    template <>
    class ParamValue <LLSD, NOT_BLOCK>
    :   public BaseBlock
    {
    public:
        typedef LLSD            value_t;
        typedef LLSD            default_value_t;

        ParamValue()
        {}

        ParamValue(const default_value_t& other)
        :   mValue(other)
        {}

        void setValue(const value_t& val) { mValue = val; }

        const value_t& getValue() const { return mValue; }
        LLSD& getValue() { return mValue; }

        // block param interface
        LL_COMMON_API bool deserializeBlock(Parser& p, Parser::name_stack_range_t& name_stack_range, bool new_name);
        LL_COMMON_API bool serializeBlock(Parser& p, Parser::name_stack_t& name_stack, const predicate_rule_t predicate_rule, const BaseBlock* diff_block = NULL) const;
        bool inspectBlock(Parser& p, Parser::name_stack_t name_stack = Parser::name_stack_t(), S32 min_count = 0, S32 max_count = S32_MAX) const
        {
            //TODO: implement LLSD params as schema type Any
            return true;
        }

    private:
        static void serializeElement(Parser& p, const LLSD& sd, Parser::name_stack_t& name_stack);

        LLSD mValue;
    };

    template<typename T>
    class CustomParamValue
    :   public Block<ParamValue<T> >
    {
    public:
        typedef enum e_value_age
        {
            VALUE_NEEDS_UPDATE,     // mValue needs to be refreshed from the block parameters
            VALUE_AUTHORITATIVE,    // mValue holds the authoritative value (which has been replicated to the block parameters via updateBlockFromValue)
            BLOCK_AUTHORITATIVE     // mValue is derived from the block parameters, which are authoritative
        } EValueAge;

        typedef TypeValues<T>           derived_t;
        typedef CustomParamValue<T>     self_t;
        typedef Block<ParamValue<T> >   block_t;
        typedef T                       default_value_t;
        typedef T                       value_t;
        typedef void                    baseblock_base_class_t;


        CustomParamValue(const default_value_t& value = T())
        :   mValue(value),
            mValueAge(VALUE_AUTHORITATIVE)
        {}

        bool deserializeBlock(Parser& parser, Parser::name_stack_range_t& name_stack_range, bool new_name)
        {
            derived_t& typed_param = static_cast<derived_t&>(*this);
            // try to parse direct value T
            if (name_stack_range.first == name_stack_range.second)
            {
                if(parser.readValue(typed_param.mValue))
                {
                    typed_param.mValueAge = VALUE_AUTHORITATIVE;
                    typed_param.updateBlockFromValue(false);

                    return true;
                }
            }

            // fall back on parsing block components for T
            return typed_param.BaseBlock::deserializeBlock(parser, name_stack_range, new_name);
        }

        bool serializeBlock(Parser& parser, Parser::name_stack_t& name_stack, const predicate_rule_t predicate_rule, const BaseBlock* diff_block = NULL) const
        {
            const derived_t& typed_param = static_cast<const derived_t&>(*this);
            const derived_t* diff_param = static_cast<const derived_t*>(diff_block);

            //std::string key = typed_param.getValueName();

            //// first try to write out name of name/value pair
            //if (!key.empty())
            //{
            //  if (!diff_param || !ParamCompare<std::string>::equals(diff_param->getValueName(), key))
            //  {
            //      return parser.writeValue(key, name_stack);
            //  }
            //}
            // then try to serialize value directly
            if (!diff_param || !ParamCompare<T>::equals(typed_param.getValue(), diff_param->getValue()))
            {

                if (parser.writeValue(typed_param.getValue(), name_stack))
                {
                    return true;
                }
                else
                {
                    //RN: *always* serialize provided components of BlockValue (don't pass diff_param on),
                    // since these tend to be viewed as the constructor arguments for the value T.  It seems
                    // cleaner to treat the uniqueness of a BlockValue according to the generated value, and
                    // not the individual components.  This way <color red="0" green="1" blue="0"/> will not
                    // be exported as <color green="1"/>, since it was probably the intent of the user to
                    // be specific about the RGB color values.  This also fixes an issue where we distinguish
                    // between rect.left not being provided and rect.left being explicitly set to 0 (same as default)

                    if (typed_param.mValueAge == VALUE_AUTHORITATIVE)
                    {
                        // if the value is authoritative but the parser doesn't accept the value type
                        // go ahead and make a copy, and splat the value out to its component params
                        // and serialize those params
                        derived_t copy(typed_param);
                        copy.updateBlockFromValue(true);
                        return copy.block_t::serializeBlock(parser, name_stack, predicate_rule, NULL);
                    }
                    else
                    {
                        return block_t::serializeBlock(parser, name_stack, predicate_rule, NULL);
                    }
                }
            }
            return false;
        }

        bool validateBlock(bool emit_errors = true) const
        {
            if (mValueAge == VALUE_NEEDS_UPDATE)
            {
                if (block_t::validateBlock(emit_errors))
                {
                    // clear stale keyword associated with old value
                    mValueAge = BLOCK_AUTHORITATIVE;
                    static_cast<derived_t*>(const_cast<self_t*>(this))->updateValueFromBlock();
                    return true;
                }
                else
                {
                    //block value incomplete, so not considered provided
                    // will attempt to revalidate on next call to isProvided()
                    return false;
                }
            }
            else
            {
                // we have a valid value in hand
                return true;
            }
        }

        // propagate change status up to enclosing block
        /*virtual*/ void paramChanged(const Param& changed_param, bool user_provided)
        {
            BaseBlock::paramChanged(changed_param, user_provided);
            if (user_provided)
            {
                // a parameter changed, so our value is out of date
                mValueAge = VALUE_NEEDS_UPDATE;
            }
        }

        void setValue(const value_t& val)
        {
            // set param version number to be up to date, so we ignore block contents
            mValueAge = VALUE_AUTHORITATIVE;
            mValue = val;
            static_cast<derived_t*>(this)->updateBlockFromValue(false);
        }

        const value_t& getValue() const
        {
            validateBlock(true);
            return mValue;
        }

        T& getValue()
        {
            validateBlock(true);
            return mValue;
        }

    protected:

        // use this from within updateValueFromBlock() to set the value without making it authoritative
        void updateValue(const value_t& value)
        {
            mValue = value;
        }

        bool mergeBlockParam(bool source_provided, bool dst_provided, BlockDescriptor& block_data, const BaseBlock& source, bool overwrite)
        {
            bool source_override = source_provided && (overwrite || !dst_provided);

            const derived_t& src_typed_param = static_cast<const derived_t&>(source);

            if (source_override && src_typed_param.mValueAge == VALUE_AUTHORITATIVE)
            {
                // copy value over
                setValue(src_typed_param.getValue());
                return true;
            }
            // merge individual parameters into destination
            if (mValueAge == VALUE_AUTHORITATIVE)
            {
                static_cast<derived_t*>(this)->updateBlockFromValue(dst_provided);
            }
            return mergeBlock(block_data, source, overwrite);
        }

        bool mergeBlock(BlockDescriptor& block_data, const BaseBlock& source, bool overwrite)
        {
            return block_t::mergeBlock(block_data, source, overwrite);
        }

    private:
        mutable T           mValue;
        mutable EValueAge   mValueAge;
    };
}


#endif // LL_LLPARAM_H