Re: [boost] detecting a constructor with a specific signature

Subject: Re: [boost] detecting a constructor with a specific signature
From: Kenny Riddile (kfriddile_at_[hidden])
Date: 2010-01-27 12:14:01

Daniel Frey wrote:
> 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
> 
> _______________________________________________
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> 

Alas, I'm using VC9.  The first declaration of select() gives me the 
following error:

error C2564: 'T' : a function-style conversion to a built-in type can 
only take one argument