Sure. I wasn't really arguing changing shared_ptr, nor did I think that there was a number of different ways to work around the problem (it was good to see the number of different ways folks would though). I was more making a point about semantic design and the fact that if one looked at all of the things that follow this paradigm, obtain some resource with a free function returning a pointer and release the resource with another free function that takes a pointer, I'd argue that more things do not allow you to release or 'delete' a null pointer than do (obviously new are free are ones that do). That's all. Mike On Nov 4, 2007, at 3:00 AM, Daniel Frey wrote:
On Sat, 2007-11-03 at 19:45 -0400, Mike Tegtmeyer wrote:
I guess if shared_ptr was to be done all over again, I think that I would argue that it should act like a pointer, ie you shouldn't be able to 'delete' a 'null' pointer - whatever delete and null mean for
Let's keep shared_ptr like it is. What you (and others) probably need is the right helper, as a quick hack it looks like this:
#include <iostream> #include <boost/shared_ptr.hpp>
struct X {};
void freeX( X* x ) { // Should not be called with a null pointer std::cout << "free " << x << std::endl; }
template< typename T > struct on_nonzero_t { typedef void (&F)( T* ); F f_;
on_nonzero_t( F f ) : f_( f ) {} void operator()( T* t ) const { if( t ) f_( t ); } };
template< typename T > on_nonzero_t< T > on_nonzero( void (&f)( T* ) ) { return on_nonzero_t< T >( f ); }
void f( X* x ) { std::cout << "x = " << x << std::endl; boost::shared_ptr< X > tmp( x, on_nonzero( freeX ) ); }
int main() { X x; f( &x );
f( 0 ); }
The naming of the helper might be crap, but anyway, hope you can make some use of it...
Regards, Daniel
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