On 27.01.2010, at 15:52, Kenny Riddile wrote:
Ya, I was already using the "flag typedef" method, but was just wondering if something non-intrusive was feasible...maybe it isn't. A compiler with 0x support isn't an option I'm afraid.
No need for C++0x if you only need a special case. Requires a good compiler, though, GCC 4.3 is not good enough, 4.4+ is. The following compiles with GCC 4.4, -ansi -pedantic, replacing decltype with sizeof :) #include <string> #include <iostream> struct Foo { Foo( const std::string& ); }; struct Bar { Bar( const std::string& ); Bar( const std::string&, Foo& ); }; template< typename T > T make(); template< int > struct result { typedef double type; }; template< typename T > typename result< sizeof T( make< const std::string& >(), make< Foo& >() ) >::type select( int ); template< typename > char select( ... ); template< typename T > struct has_foo_ctor { enum { value = sizeof select< T >( 0 ) > 1 }; }; int main() { std::cout << has_foo_ctor< Foo >::value << std::endl; std::cout << has_foo_ctor< Bar >::value << std::endl; } Regards, Daniel