雖然這個職位是幾年,我可能能夠添加一些有用的東西。雖然我會說在原始文章中該類的設計看起來不太好,但是有時候嵌入類能夠訪問包含類是有用的。這可以很容易地完成而不需要存儲額外的指針。下面是一個例子。它應該像我從一些現有的代碼中拿出來一樣工作,並且改變了一些名字。關鍵是EmbeddorOf宏。奇蹟般有效。
//////////////////// .h file /////////////////////// //
struct IReferenceCounted
{
virtual unsigned long AddRef() = 0;
virtual unsigned long Release() = 0;
};
struct IFoo : public IReferenceCounted
{
};
class Foo : public IFoo
{
public:
static IFoo* Create();
static IFoo* Create(IReferenceCounted* outer, IReferenceCounted** inner);
private:
Foo();
Foo(IReferenceCounted* outer);
~Foo();
// IReferenceCounted
unsigned long AddRef();
unsigned long Release();
private:
struct EIReferenceCounted : IReferenceCounted
{
// IReferenceCounted
unsigned long AddRef();
unsigned long Release();
} _inner;
unsigned long _refs;
IReferenceCounted* _outer;
};
////////////////。CPP文件/////////////////
#include <stdio.h>
#include <stddef.h>
#include "Foo.h"
#define EmbeddorOf(class, member, this) \
(class *) ((char *) this - offsetof(class, member))
// Foo
Foo::Foo() : _refs(1), _outer(&this->_inner)
{
}
Foo::Foo(IReferenceCounted* outer) : _refs(1), _outer(outer)
{
}
Foo::~Foo()
{
printf("Foo::~Foo()\n");
}
IFoo* Foo::Create()
{
return new Foo();
}
IFoo* Foo::Create(IReferenceCounted* outer, IReferenceCounted** inner)
{
Foo* foo = new Foo(outer);
*inner = &foo->_inner;
return (IFoo*) foo;
}
// IReferenceCounted
unsigned long Foo::AddRef()
{
printf("Foo::AddRef()\n");
return this->_outer->AddRef();
}
unsigned long Foo::Release()
{
printf("Foo::Release()\n");
return this->_outer->Release();
}
// Inner IReferenceCounted
unsigned long Foo::EIReferenceCounted::AddRef()
{
Foo* pThis = EmbeddorOf(Foo, _inner, this);
return ++pThis->_refs;
}
unsigned long Foo::EIReferenceCounted::Release()
{
Foo* pThis = EmbeddorOf(Foo, _inner, this);
unsigned long refs = --pThis->_refs;
if (refs == 0)
{
// Artifically increment so that we won't try to destroy multiple
// times in the event that our destructor causes AddRef()'s or
// Releases().
pThis->_refs = 1;
delete pThis;
}
return refs;
}
尼克
從Java即將:-) – 2008-10-25 21:59:01