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- /*
- @Copyright Barrett Adair 2015-2017
- Distributed under the Boost Software License, Version 1.0.
- (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
- */
- #ifndef BOOST_CLBL_TRTS_HAS_VOID_RETURN_HPP
- #define BOOST_CLBL_TRTS_HAS_VOID_RETURN_HPP
- #include <boost/callable_traits/detail/core.hpp>
- namespace boost { namespace callable_traits {
- //[ has_void_return_hpp
- /*`[section:ref_has_void_return has_void_return]
- [heading Header]
- ``#include <boost/callable_traits/has_void_return.hpp>``
- [heading Definition]
- */
- // inherits from either std::true_type or std::false_type
- template<typename T>
- struct has_void_return;
- //<-
- template<typename T>
- struct has_void_return
- : std::is_same<typename detail::traits<
- detail::shallow_decay<T>>::return_type, void> {};
- #ifdef BOOST_CLBL_TRTS_DISABLE_VARIABLE_TEMPLATES
- template<typename T>
- struct has_void_return_v {
- static_assert(std::is_same<T, detail::dummy>::value,
- "Variable templates not supported on this compiler.");
- };
- #else
- //->
- // only available when variable templates are supported
- template<typename T>
- //<-
- BOOST_CLBL_TRAITS_INLINE_VAR
- //->
- constexpr bool has_void_return_v = //see below
- //<-
- std::is_same<typename detail::traits<
- detail::shallow_decay<T>>::return_type, void>::value;
- #endif
- }} // namespace boost::callable_traits
- //->
- /*`
- [heading Constraints]
- * none
- [heading Behavior]
- * `std::false_type` is inherited by `has_void_return<T>` and is aliased by `typename has_void_return<T>::type`, except when one of the following criteria is met, in which case `std::true_type` would be similarly inherited and aliased:
- * `T` is a function, function pointer, or function reference where the function's return type is `void`.
- * `T` is a pointer to a member function whose return type is `void`.
- * `T` is a function object with a non-overloaded `operator()`, where the `operator()` function returns `void`.
- * On compilers that support variable templates, `has_void_return_v<T>` is equivalent to `has_void_return<T>::value`.
- [heading Input/Output Examples]
- [table
- [[`T`] [`has_void_return_v<T>`]]
- [[`void()`] [`true`]]
- [[`void(int) const`] [`true`]]
- [[`void(* const &)()`] [`true`]]
- [[`void(&)()`] [`true`]]
- [[`void(foo::*)() const`] [`true`]]
- [[`int(*)()`] [`false`]]
- [[`int(*&)()`] [`false`]]
- [[`int`] [`false`]]
- [[`int foo::*`] [`false`]]
- [[`void* foo::*`] [`false`]]
- ]
- [heading Example Program]
- [import ../example/has_void_return.cpp]
- [has_void_return]
- [endsect]
- */
- //]
- #endif
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