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/**
* @file llsafehandle.h
* @brief Reference-counted object where Object() is valid, not NULL.
*
* $LicenseInfo:firstyear=2002&license=viewerlgpl$
* 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 LLSAFEHANDLE_H
#define LLSAFEHANDLE_H
#include "llerror.h" // *TODO: consider eliminating this
#include "llsingleton.h"
// Expands LLPointer to return a pointer to a special instance of class Type instead of NULL.
// This is useful in instances where operations on NULL pointers are semantically safe and/or
// when error checking occurs at a different granularity or in a different part of the code
// than when referencing an object via a LLSafeHandle.
template <class Type>
class LLSafeHandle
{
public:
LLSafeHandle() :
mPointer(NULL)
{
}
LLSafeHandle(Type* ptr) :
mPointer(NULL)
{
assign(ptr);
}
LLSafeHandle(const LLSafeHandle<Type>& ptr) :
mPointer(NULL)
{
assign(ptr.mPointer);
}
// support conversion up the type hierarchy. See Item 45 in Effective C++, 3rd Ed.
template<typename Subclass>
LLSafeHandle(const LLSafeHandle<Subclass>& ptr) :
mPointer(NULL)
{
assign(ptr.get());
}
~LLSafeHandle()
{
unref();
}
const Type* operator->() const { return nonNull(mPointer); }
Type* operator->() { return nonNull(mPointer); }
Type* get() const { return mPointer; }
void clear() { assign(NULL); }
// we disallow these operations as they expose our null objects to direct manipulation
// and bypass the reference counting semantics
//const Type& operator*() const { return *nonNull(mPointer); }
//Type& operator*() { return *nonNull(mPointer); }
operator BOOL() const { return mPointer != NULL; }
operator bool() const { return mPointer != NULL; }
bool operator!() const { return mPointer == NULL; }
bool isNull() const { return mPointer == NULL; }
bool notNull() const { return mPointer != NULL; }
operator Type*() const { return mPointer; }
operator const Type*() const { return mPointer; }
bool operator !=(Type* ptr) const { return (mPointer != ptr); }
bool operator ==(Type* ptr) const { return (mPointer == ptr); }
bool operator ==(const LLSafeHandle<Type>& ptr) const { return (mPointer == ptr.mPointer); }
bool operator < (const LLSafeHandle<Type>& ptr) const { return (mPointer < ptr.mPointer); }
bool operator > (const LLSafeHandle<Type>& ptr) const { return (mPointer > ptr.mPointer); }
LLSafeHandle<Type>& operator =(Type* ptr)
{
assign(ptr);
return *this;
}
LLSafeHandle<Type>& operator =(const LLSafeHandle<Type>& ptr)
{
assign(ptr.mPointer);
return *this;
}
// support assignment up the type hierarchy. See Item 45 in Effective C++, 3rd Ed.
template<typename Subclass>
LLSafeHandle<Type>& operator =(const LLSafeHandle<Subclass>& ptr)
{
assign(ptr.get());
return *this;
}
protected:
void ref()
{
if (mPointer)
{
mPointer->ref();
}
}
void unref()
{
if (mPointer)
{
Type *tempp = mPointer;
mPointer = NULL;
tempp->unref();
if (mPointer != NULL)
{
LL_WARNS() << "Unreference did assignment to non-NULL because of destructor" << LL_ENDL;
unref();
}
}
}
void assign(Type* ptr)
{
if( mPointer != ptr )
{
unref();
mPointer = ptr;
ref();
}
}
// Define an LLSingleton whose sole purpose is to hold a "null instance"
// of the subject Type: the canonical instance to dereference if this
// LLSafeHandle actually holds a null pointer. We use LLSingleton
// specifically so that the "null instance" can be cleaned up at a well-
// defined time, specifically LLSingletonBase::deleteAll().
// Of course, as with any LLSingleton, the "null instance" is only
// instantiated on demand -- in this case, if you actually try to
// dereference an LLSafeHandle containing null.
class NullInstanceHolder: public LLSingleton<NullInstanceHolder>
{
LLSINGLETON_EMPTY_CTOR(NullInstanceHolder);
public:
Type mNullInstance;
};
static Type* nonNull(Type* ptr)
{
return ptr? ptr : &NullInstanceHolder::instance().mNullInstance;
}
protected:
Type* mPointer;
};
#endif
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