[EnableIf?] Seeking an example....
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. It might have been written by Eric. I can't find it now,maybe it's not there any more, but if anyone can point me to it I'd really appreciate it! Thanks in advance, - Rob.
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 compile-time detection of whether the object has some member function with a given signature or not. You can detect mostly everything but constructors and member-only operators, actually. It's too bad there isn't a Boost library to do just that. It's true that with concepts, though, it becomes less useful. There are probably bits in some places in Boost but I never knew where they were.
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 <class T, void (T::*)() const > struct test_for_member_go{ }; template<class T> static Found test_for_go(test_for_member_go<T,&T::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.
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Joel Falcou -
Mathias Gaunard -
Robert Jones