Thanks, Sylvain to point to that. :)The use case is similar and a little different.Boost Concept Check will fail if not meet requirements.I would like a way to test it and return boolean. For example, I would like do something like below: struct default_foo{ void foo();}; struct user_foo{ void foo();}; template <typename T>void call_foo(typename if_::value, T, default_foo>::type u){ u.foo();} Thanks,Wei

Date: Sat, 22 Nov 2014 22:44:49 +0800 From: sylvain.bougerel.devel@gmail.com To: boost@lists.boost.org Subject: Re: [boost] Is there interest in a library for testing existence of a function member of class?

Hi Wei,

Have you checked Boost Concept Check library, it looks like it could fit your use case.

Regards, Sylvain On 22 Nov 2014 22:33, "胡维" wrote:

...

Hi, I am looking for how to test if a function member of class exist or not in compile time.I did not find a solution by google so I wrote a piece of code for it.Please let me know if it's already in boost. :) Synopsis class Bar { public: Bar(int); };

class Foo { public: Foo(int); int foo(Bar); };

// create struct 'has_foo' which is used to test function member 'foo'.HAS_FUNCTION_MEMBER(foo)

int main() { assert((!has_foo::value)); assert((has_foo::value)); return 0; } The code is in my gisthttps://gist.github.com/wehu/1987f716074904d26cf0 The code only checks if the function is compatible with expected, but not require to be exact same. Thanks,Wei

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oh, thanks! That's almost same as mine. :) Wei

Date: Sat, 22 Nov 2014 23:36:48 +0800 From: tongari95@gmail.com To: boost@lists.boost.org Subject: Re: [boost] Is there interest in a library for testing existence of a function member of class?

2014-11-22 17:36 GMT+08:00 胡维 :

...

Hi, I am looking for how to test if a function member of class exist or not in compile time.I did not find a solution by google so I wrote a piece of code for it.Please let me know if it's already in boost. :)

Yes, it's in Boost.TTI: http://tinyurl.com/k3y5x8l

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Phil Endecott writes:

Has anyone ever worked out how to do this without having to specify the type? E.g. with BOOST_TTI_HAS_MEMBER_DATA I need to write something like

has_member_data_fieldname::value;

The most recent time I needed something like this, I wanted to test whether a struct contained a field with a particular name that was convertible to a float (I think float or int16_t in that case). I would have been happy with a test for a field with that name of any type. But I couldn't work out how to do it. Any ideas?

In C++11, decltype and expression SFINAE make this trait very trivial. (decltype is enough to not need the signature.) Regards

The most recent time I needed something like this, I wanted to test whether a struct contained a field with a particular name that was convertible to a float (I think float or int16_t in that case). I would have been happy with a test for a field with that name of any type. But I couldn't work out how to do it. Any ideas?

I think below code(incomplete) can test a field with a name of any type. template <int c>struct enable{ typedef void type;}; template <typename T>struct wrapper{ static T value;}; template struct has_foo_impl{ enum { value = false };}; template <typename T>struct has_foo_impl::type>{ enum { value = true };}; template <typename T>struct has_foo : has_foo_impl<const T> {}; struct a{};struct b{ int foo; }; #include <iostream> int main (){ std::cout << has_foo<a>::value << std::endl; std::cout << has_foo<b>::value << std::endl; return 0;}

...

...

Yes, it's in Boost.TTI: http://tinyurl.com/k3y5x8l

Has anyone ever worked out how to do this without having to specify the type? E.g. with BOOST_TTI_HAS_MEMBER_DATA I need to write something like

has_member_data_fieldname::value;

The most recent time I needed something like this, I wanted to test whether a struct contained a field with a particular name that was convertible to a float (I think float or int16_t in that case). I would have been happy with a test for a field with that name of any type. But I couldn't work out how to do it. Any ideas?

I just realized that BOOST_TTI_HAS_MEMBER_FUNCTION is not exactly same as mine.BOOST_TTI_HAS_MEMBER_FUNCTION will check the type signature and only return true if it's exactly match. I would like to test if a member function of class is 'applicable'. For example, below code will print 0, but I expect to get 1.BOOST_TTI_HAS_MEMBER_FUNCTION(foo) class a{public: int foo(int);}; int main(){ std::cout << has_member_function_foo::value << std::endl; return 0;}