Re: [Boost-users] [EnableIf?] Seeking an example....

17 Sep 2008

      Mathias Gaunard a écrit :
...
Robert Jones wrote:
...
Somewhere in the Boost headers, or maybe the Boost documentation I 
have seen a
bit of code which uses SFINAE, and also possibly the enable_if header
to select either
a find class method or find global template depending on what's 
available.
That's something that was already explained indeed.
Here is a way to do it. Let's say you want to test for presence of a 
go() method 
with the following prototype :
void go();

in any type :

typedef char NotFound; struct Found { char x[2]; };

template  struct test_for_member_go{ };
template<class T> static Found       
test_for_go(test_for_member_go*);
template<class T> static NotFound test_for_go( ... );

template<class T>
struct test
{
  static const bool value = (sizeof( test_for_go<T>( 0 ) ) == 
sizeof(Found));
 typedef boost::mpl::bool_<value> type;
};

I *think* it can be made in a macro using BOOST_TYPEOF and some __LINE__ 
shenanigans to generate this for any method of any prototype.

Re: [Boost-users] [EnableIf?] Seeking an example....

Joel Falcou