Re: [boost] intrusive_ptr and overloading not working under VC++ 8

10 Dec 2005


      Sorry,
I posted the wrong code. Here is the code causing the ambiguouty:

class RefCnt {};

inline void intrusive_ptr_add_ref(RefCnt *aObj);
inline void intrusive_ptr_release(RefCnt *aObj);

class GLTexture: public RefCnt {};
class GLOffscreenTexture: public GLTexture {};
class GLRenderBuffer: public RefCnt {};

typedef intrusive_ptr<GLTexture> GLTexturePtr;
typedef intrusive_ptr<GLOffscreenTexture> GLOffscreenTexturePtr;
typedef intrusive_ptr<GLRenderBuffer> GLRenderBufferPtr;

void attachTarget(GLTexturePtr aTexture);
void attachTarget(GLRenderBufferPtr aBuffer);

int main()
{
	GLOffscreenTexturePtr ptr = new GLOffscreenTexture;
	attachTarget(ptr);
}

Produces:
...\tst.cpp(...) : error C2668: 'attachTarget' : ambiguous call to 
overloaded function


Peter Dimov wrote:
...
Stefan Popov wrote:
...
I ran onto a problem when using intrusive_ptr, overloading and MS
visual studio 8
All my classes derive a reference counted class RefCnt. For example:
class GLTexture : public RefCnt {...};
class GLRenderBuffer : public RefCnt {...};
I define smart pointers using the intrusive_ptr class:
typedef boost::intrusive_ptr<GLTexture> GLTexturePtr;
typedef boost::intrusive_ptr<GLRenderBuffer> GLRenderBufferPtr;
Than I define a function accepting both GLTexturePtr and
GLRenderBufferPtr :
void attachTarget(GLTexturePtr aTexture);
void attachTarget(GLRenderBufferPtr aBuffer);
invoking <code>attach(new GLTexture)</code> leads to an error:
ambiguous function call.
The reason is in the contructor of intrusive_ptr:
  template<class U> intrusive_ptr(intrusive_ptr<U> const & rhs) ...
which allows an invocation with an unrelated pointer.
This program:
#include <boost/intrusive_ptr.hpp>
class RefCnt
{
};
void intrusive_ptr_add_ref( RefCnt * );
void intrusive_ptr_release( RefCnt * );
class GLTexture: public RefCnt
{
};
class GLRenderBuffer: public RefCnt
{
};
typedef boost::intrusive_ptr<GLTexture> GLTexturePtr;
typedef boost::intrusive_ptr<GLRenderBuffer> GLRenderBufferPtr;
void attachTarget(GLTexturePtr aTexture);
void attachTarget(GLRenderBufferPtr aBuffer);
int main()
{
    attachTarget( new GLTexture );
}
compiles for me under MSVC 8.
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