62 lines
3.8 KiB
C++
62 lines
3.8 KiB
C++
|
// Copyright (c) 2009-2016 Vladimir Batov.
|
||
|
|
// Use, modification and distribution are subject to the Boost Software License,
|
||
|
|
// Version 1.0. See http://www.boost.org/LICENSE_1_0.txt.
|
||
|
|
|
||
|
|
#ifndef BOOST_CONVERT_HAS_MEMBER_HPP
|
||
|
|
#define BOOST_CONVERT_HAS_MEMBER_HPP
|
||
|
|
|
||
|
|
#include <boost/type_traits/remove_const.hpp>
|
||
|
|
#include <boost/type_traits/detail/yes_no_type.hpp>
|
||
|
|
|
||
|
|
// This macro allows to check if a type has a member named "__member_name__"...
|
||
|
|
// ... regardless of the signature. If takes advantage of the following behavior related to
|
||
|
|
// function resolution. Say, both, foo and base, declare a method with the same name "func":
|
||
|
|
//
|
||
|
|
// struct foo { int func (int, int) { return 0; } };
|
||
|
|
// struct base { void func () {} };
|
||
|
|
// struct mixin : public foo, public base {};
|
||
|
|
//
|
||
|
|
// Now, if we inherit from both -- foo and base -- classes, then the following calls will fail
|
||
|
|
// mixin_ptr(0)->func();
|
||
|
|
// mixin_ptr(0)->func(5, 5);
|
||
|
|
// with the error message (gcc): request for member func is ambiguous
|
||
|
|
// regardless if we provide any arguments or not even though one might expect that
|
||
|
|
// arg-based signature resolution might kick in. The only way to deploy those methods is:
|
||
|
|
//
|
||
|
|
// mixin_ptr(0)->foo::func();
|
||
|
|
// mixin_ptr(0)->base::func(5, 5);
|
||
|
|
//
|
||
|
|
// C2. The actual signature of __member_name__ is not taken into account. If
|
||
|
|
// __T__::__member_name__(any-signature) exists, then the introduced base::__member_name__
|
||
|
|
// will cause mixin->__member_name__() call to fail to compile (due to ambiguity).
|
||
|
|
// C3. &U::__member_name__ (a.k.a. &mixin::__member_name__)
|
||
|
|
// has the type of func_type only if __T__::__member_name__ does not exist.
|
||
|
|
// If __T__::member_name does exist, then mixin::__member_name__ is ambiguous
|
||
|
|
// and "yes_type test (...)" kicks in instead.
|
||
|
|
// C4. Need to find some unique/ugly name so that it does not clash if this macro is
|
||
|
|
// used inside some other template class;
|
||
|
|
|
||
|
|
#define BOOST_DECLARE_HAS_MEMBER(__trait_name__, __member_name__) \
|
||
|
|
\
|
||
|
|
template <typename __boost_has_member_T__> /*C4*/ \
|
||
|
|
class __trait_name__ \
|
||
|
|
{ \
|
||
|
|
typedef typename ::boost::remove_const<__boost_has_member_T__>::type check_type; \
|
||
|
|
typedef ::boost::type_traits::yes_type yes_type; \
|
||
|
|
typedef ::boost::type_traits:: no_type no_type; \
|
||
|
|
\
|
||
|
|
struct base { void __member_name__(/*C2*/) {}}; \
|
||
|
|
struct mixin : public base, public check_type {}; \
|
||
|
|
\
|
||
|
|
template <void (base::*)()> struct aux {}; \
|
||
|
|
\
|
||
|
|
template <typename U> static no_type test(aux<&U::__member_name__>*); /*C3*/ \
|
||
|
|
template <typename U> static yes_type test(...); \
|
||
|
|
\
|
||
|
|
public: \
|
||
|
|
\
|
||
|
|
BOOST_STATIC_CONSTANT(bool, value = (sizeof(yes_type) == sizeof(test<mixin>(0)))); \
|
||
|
|
}
|
||
|
|
|
||
|
|
#endif // BOOST_CONVERT_HAS_MEMBER_HPP
|