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author | Richard Linden <none@none> | 2013-10-01 14:28:39 -0700 |
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committer | Richard Linden <none@none> | 2013-10-01 14:28:39 -0700 |
commit | 59628d6f85deed89cb35d9343183069cfccd13c0 (patch) | |
tree | 6b4c35053c2291fd5ff1cccedf86bbd76ce78e1d /indra/llcommon/lllazy.h | |
parent | ad777b46d0fe5d790e43efb1771e9f64f3ad3dfb (diff) | |
parent | 9e486f6c6abbee6cb41ba9a6271d8a025ad924ef (diff) |
Automated merge with http://bitbucket.org/lindenlab/viewer-release
Diffstat (limited to 'indra/llcommon/lllazy.h')
-rwxr-xr-x | indra/llcommon/lllazy.h | 399 |
1 files changed, 0 insertions, 399 deletions
diff --git a/indra/llcommon/lllazy.h b/indra/llcommon/lllazy.h deleted file mode 100755 index 5f3bbce79e..0000000000 --- a/indra/llcommon/lllazy.h +++ /dev/null @@ -1,399 +0,0 @@ -/** - * @file lllazy.h - * @author Nat Goodspeed - * @date 2009-01-22 - * @brief Lazy instantiation of specified type. Useful in conjunction with - * Michael Feathers's "Extract and Override Getter" ("Working - * Effectively with Legacy Code", p. 352). - * - * Quoting his synopsis of steps on p.355: - * - * 1. Identify the object you need a getter for. - * 2. Extract all of the logic needed to create the object into a getter. - * 3. Replace all uses of the object with calls to the getter, and initialize - * the reference that holds the object to null in all constructors. - * 4. Add the first-time logic to the getter so that the object is constructed - * and assigned to the reference whenever the reference is null. - * 5. Subclass the class and override the getter to provide an alternative - * object for testing. - * - * It's the second half of bullet 3 (3b, as it were) that bothers me. I find - * it all too easy to imagine adding pointer initializers to all but one - * constructor... the one not exercised by my tests. That suggested using - * (e.g.) boost::scoped_ptr<MyObject> so you don't have to worry about - * destroying it either. - * - * However, introducing additional machinery allows us to encapsulate bullet 4 - * as well. - * - * $LicenseInfo:firstyear=2009&license=viewerlgpl$ - * 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 - * $/LicenseInfo$ - */ - -#if ! defined(LL_LLLAZY_H) -#define LL_LLLAZY_H - -#include <boost/function.hpp> -#include <boost/scoped_ptr.hpp> -#include <boost/lambda/construct.hpp> -#include <stdexcept> - -/// LLLazyCommon simply factors out of LLLazy<T> things that don't depend on -/// its template parameter. -class LLLazyCommon -{ -public: - /** - * This exception is thrown if you try to replace an LLLazy<T>'s factory - * (or T* instance) after it already has an instance in hand. Since T - * might well be stateful, we can't know the effect of silently discarding - * and replacing an existing instance, so we disallow it. This facility is - * intended for testing, and in a test scenario we can definitely control - * that. - */ - struct InstanceChange: public std::runtime_error - { - InstanceChange(const std::string& what): std::runtime_error(what) {} - }; - -protected: - /** - * InstanceChange might be appropriate in a couple of different LLLazy<T> - * methods. Factor out the common logic. - */ - template <typename PTR> - static void ensureNoInstance(const PTR& ptr) - { - if (ptr) - { - // Too late: we've already instantiated the lazy object. We don't - // know whether it's stateful or not, so it's not safe to discard - // the existing instance in favor of a replacement. - throw InstanceChange("Too late to replace LLLazy instance"); - } - } -}; - -/** - * LLLazy<T> is useful when you have an outer class Outer that you're trying - * to bring under unit test, that contains a data member difficult to - * instantiate in a test harness. Typically the data member's class Inner has - * many thorny dependencies. Feathers generally advocates "Extract and - * Override Factory Method" (p. 350). But in C++, you can't call a derived - * class override of a virtual method from the derived class constructor, - * which limits applicability of "Extract and Override Factory Method." For - * such cases Feathers presents "Extract and Override Getter" (p. 352). - * - * So we'll assume that your class Outer contains a member like this: - * @code - * Inner mInner; - * @endcode - * - * LLLazy<Inner> can be used to replace this member. You can directly declare: - * @code - * LLLazy<Inner> mInner; - * @endcode - * and change references to mInner accordingly. - * - * (Alternatively, you can add a base class of the form - * <tt>LLLazyBase<Inner></tt>. This is discussed further in the LLLazyBase<T> - * documentation.) - * - * LLLazy<T> binds a <tt>boost::scoped_ptr<T></tt> and a factory functor - * returning T*. You can either bind that functor explicitly or let it default - * to the expression <tt>new T()</tt>. - * - * As long as LLLazy<T> remains unreferenced, its T remains uninstantiated. - * The first time you use get(), <tt>operator*()</tt> or <tt>operator->()</tt> - * it will instantiate its T and thereafter behave like a pointer to it. - * - * Thus, any existing reference to <tt>mInner.member</tt> should be replaced - * with <tt>mInner->member</tt>. Any simple reference to @c mInner should be - * replaced by <tt>*mInner</tt>. - * - * (If the original declaration was a pointer initialized in Outer's - * constructor, e.g. <tt>Inner* mInner</tt>, so much the better. In that case - * you should be able to drop in <tt>LLLazy<Inner></tt> without much change.) - * - * The support for "Extract and Override Getter" lies in the fact that you can - * replace the factory functor -- or provide an explicit T*. Presumably this - * is most useful from a test subclass -- which suggests that your @c mInner - * member should be @c protected. - * - * Note that <tt>boost::lambda::new_ptr<T>()</tt> makes a dandy factory - * functor, for either the set() method or LLLazy<T>'s constructor. If your T - * requires constructor arguments, use an expression more like - * <tt>boost::lambda::bind(boost::lambda::new_ptr<T>(), arg1, arg2, ...)</tt>. - * - * Of course the point of replacing the functor is to substitute a class that, - * though referenced as Inner*, is not an Inner; presumably this is a testing - * subclass of Inner (e.g. TestInner). Thus your test subclass TestOuter for - * the containing class Outer will contain something like this: - * @code - * class TestOuter: public Outer - * { - * public: - * TestOuter() - * { - * // mInner must be 'protected' rather than 'private' - * mInner.set(boost::lambda::new_ptr<TestInner>()); - * } - * ... - * }; - * @endcode - */ -template <typename T> -class LLLazy: public LLLazyCommon -{ -public: - /// Any nullary functor returning T* will work as a Factory - typedef boost::function<T* ()> Factory; - - /// The default LLLazy constructor uses <tt>new T()</tt> as its Factory - LLLazy(): - mFactory(boost::lambda::new_ptr<T>()) - {} - - /// Bind an explicit Factory functor - LLLazy(const Factory& factory): - mFactory(factory) - {} - - /// Reference T, instantiating it if this is the first access - const T& get() const - { - if (! mInstance) - { - // use the bound Factory functor - mInstance.reset(mFactory()); - } - return *mInstance; - } - - /// non-const get() - T& get() - { - return const_cast<T&>(const_cast<const LLLazy<T>*>(this)->get()); - } - - /// operator*() is equivalent to get() - const T& operator*() const { return get(); } - /// operator*() is equivalent to get() - T& operator*() { return get(); } - - /** - * operator->() must return (something resembling) T*. It's tempting to - * return the underlying boost::scoped_ptr<T>, but that would require - * breaking out the lazy-instantiation logic from get() into a common - * private method. Assume the pointer used for operator->() access is very - * short-lived. - */ - const T* operator->() const { return &get(); } - /// non-const operator->() - T* operator->() { return &get(); } - - /// set(Factory). This will throw InstanceChange if mInstance has already - /// been set. - void set(const Factory& factory) - { - ensureNoInstance(mInstance); - mFactory = factory; - } - - /// set(T*). This will throw InstanceChange if mInstance has already been - /// set. - void set(T* instance) - { - ensureNoInstance(mInstance); - mInstance.reset(instance); - } - -private: - Factory mFactory; - // Consider an LLLazy<T> member of a class we're accessing by const - // reference. We want to allow even const methods to touch the LLLazy<T> - // member. Hence the actual pointer must be mutable because such access - // might assign it. - mutable boost::scoped_ptr<T> mInstance; -}; - -#if (! defined(__GNUC__)) || (__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ > 3) -// Not gcc at all, or a gcc more recent than gcc 3.3 -#define GCC33 0 -#else -#define GCC33 1 -#endif - -/** - * LLLazyBase<T> wraps LLLazy<T>, giving you an alternative way to replace - * <tt>Inner mInner;</tt>. Instead of coding <tt>LLLazy<Inner> mInner</tt>, - * you can add LLLazyBase<Inner> to your Outer class's bases, e.g.: - * @code - * class Outer: public LLLazyBase<Inner> - * { - * ... - * }; - * @endcode - * - * This gives you @c public get() and @c protected set() methods without - * having to make your LLLazy<Inner> member @c protected. The tradeoff is that - * you must access the wrapped LLLazy<Inner> using get() and set() rather than - * with <tt>operator*()</tt> or <tt>operator->()</tt>. - * - * This mechanism can be used for more than one member, but only if they're of - * different types. That is, you can replace: - * @code - * DifficultClass mDifficult; - * AwkwardType mAwkward; - * @endcode - * with: - * @code - * class Outer: public LLLazyBase<DifficultClass>, public LLLazyBase<AwkwardType> - * { - * ... - * }; - * @endcode - * but for a situation like this: - * @code - * DifficultClass mMainDifficult, mAuxDifficult; - * @endcode - * you should directly embed LLLazy<DifficultClass> (q.v.). - * - * For multiple LLLazyBase bases, e.g. the <tt>LLLazyBase<DifficultClass>, - * LLLazyBase<AwkwardType></tt> example above, access the relevant get()/set() - * as (e.g.) <tt>LLLazyBase<DifficultClass>::get()</tt>. (This is why you - * can't have multiple LLLazyBase<T> of the same T.) For a bit of syntactic - * sugar, please see getLazy()/setLazy(). - */ -template <typename T> -class LLLazyBase -{ -public: - /// invoke default LLLazy constructor - LLLazyBase() {} - /// make wrapped LLLazy bind an explicit Factory - LLLazyBase(const typename LLLazy<T>::Factory& factory): - mInstance(factory) - {} - - /// access to LLLazy::get() - T& get() { return *mInstance; } - /// access to LLLazy::get() - const T& get() const { return *mInstance; } - -protected: - // see getLazy()/setLazy() - #if (! GCC33) - template <typename T2, class MYCLASS> friend T2& getLazy(MYCLASS* this_); - template <typename T2, class MYCLASS> friend const T2& getLazy(const MYCLASS* this_); - #else // gcc 3.3 - template <typename T2, class MYCLASS> friend T2& getLazy(const MYCLASS* this_); - #endif // gcc 3.3 - template <typename T2, class MYCLASS> friend void setLazy(MYCLASS* this_, T2* instance); - template <typename T2, class MYCLASS> - friend void setLazy(MYCLASS* this_, const typename LLLazy<T2>::Factory& factory); - - /// access to LLLazy::set(Factory) - void set(const typename LLLazy<T>::Factory& factory) - { - mInstance.set(factory); - } - - /// access to LLLazy::set(T*) - void set(T* instance) - { - mInstance.set(instance); - } - -private: - LLLazy<T> mInstance; -}; - -/** - * @name getLazy()/setLazy() - * Suppose you have something like the following: - * @code - * class Outer: public LLLazyBase<DifficultClass>, public LLLazyBase<AwkwardType> - * { - * ... - * }; - * @endcode - * - * Your methods can reference the @c DifficultClass instance using - * <tt>LLLazyBase<DifficultClass>::get()</tt>, which is admittedly a bit ugly. - * Alternatively, you can write <tt>getLazy<DifficultClass>(this)</tt>, which - * is somewhat more straightforward to read. - * - * Similarly, - * @code - * LLLazyBase<DifficultClass>::set(new TestDifficultClass()); - * @endcode - * could instead be written: - * @code - * setLazy<DifficultClass>(this, new TestDifficultClass()); - * @endcode - * - * @note - * I wanted to provide getLazy() and setLazy() without explicitly passing @c - * this. That would imply making them methods on a base class rather than free - * functions. But if <tt>LLLazyBase<T></tt> derives normally from (say) @c - * LLLazyGrandBase providing those methods, then unqualified getLazy() would - * be ambiguous: you'd have to write <tt>LLLazyBase<T>::getLazy<T>()</tt>, - * which is even uglier than <tt>LLLazyBase<T>::get()</tt>, and therefore - * pointless. You can make the compiler not care which @c LLLazyGrandBase - * instance you're talking about by making @c LLLazyGrandBase a @c virtual - * base class of @c LLLazyBase. But in that case, - * <tt>LLLazyGrandBase::getLazy<T>()</tt> can't access - * <tt>LLLazyBase<T>::get()</tt>! - * - * We want <tt>getLazy<T>()</tt> to access <tt>LLLazyBase<T>::get()</tt> as if - * in the lexical context of some subclass method. Ironically, free functions - * let us do that better than methods on a @c virtual base class -- but that - * implies passing @c this explicitly. So be it. - */ -//@{ -#if (! GCC33) -template <typename T, class MYCLASS> -T& getLazy(MYCLASS* this_) { return this_->LLLazyBase<T>::get(); } -template <typename T, class MYCLASS> -const T& getLazy(const MYCLASS* this_) { return this_->LLLazyBase<T>::get(); } -#else // gcc 3.3 -// For const-correctness, we really should have two getLazy() variants: one -// accepting const MYCLASS* and returning const T&, the other accepting -// non-const MYCLASS* and returning non-const T&. This works fine on the Mac -// (gcc 4.0.1) and Windows (MSVC 8.0), but fails on our Linux 32-bit Debian -// Sarge stations (gcc 3.3.5). Since I really don't know how to beat that aging -// compiler over the head to make it do the right thing, I'm going to have to -// move forward with the wrong thing: a single getLazy() function that accepts -// const MYCLASS* and returns non-const T&. -template <typename T, class MYCLASS> -T& getLazy(const MYCLASS* this_) { return const_cast<MYCLASS*>(this_)->LLLazyBase<T>::get(); } -#endif // gcc 3.3 -template <typename T, class MYCLASS> -void setLazy(MYCLASS* this_, T* instance) { this_->LLLazyBase<T>::set(instance); } -template <typename T, class MYCLASS> -void setLazy(MYCLASS* this_, const typename LLLazy<T>::Factory& factory) -{ - this_->LLLazyBase<T>::set(factory); -} -//@} - -#endif /* ! defined(LL_LLLAZY_H) */ |