ceph/src/boost/boost/callable_traits/return_type.hpp

   1 /*
   2
   3 @Copyright Barrett Adair 2015-2017
   4
   5 Distributed under the Boost Software License, Version 1.0.
   6 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
   7
   8 */
   9
  10 #ifndef BOOST_CLBL_TRTS_RESULT_OF_HPP
  11 #define BOOST_CLBL_TRTS_RESULT_OF_HPP
  12
  13 #include <boost/callable_traits/detail/core.hpp>
  14
  15 namespace boost { namespace callable_traits {
  16
  17 BOOST_CLBL_TRTS_DEFINE_SFINAE_ERROR_ORIGIN(return_type)
  18 BOOST_CLBL_TRTS_SFINAE_MSG(return_type, unable_to_determine_return_type)
  19
  20 //[ return_type_hpp
  21 /*`
  22 [section:ref_return_type return_type]
  23 [heading Header]
  24 ``#include <boost/callable_traits/return_type.hpp>``
  25 [heading Definition]
  26 */
  27
  28 template<typename T>
  29 using return_type_t = //see below
  30 //<-
  31     detail::try_but_fail_if_invalid<
  32         typename detail::traits<detail::shallow_decay<T>>::return_type,
  33         unable_to_determine_return_type>;
  34
  35 namespace detail {
  36
  37     template<typename T, typename = std::false_type>
  38     struct return_type_impl {};
  39
  40     template<typename T>
  41     struct return_type_impl <T, typename std::is_same<
  42         return_type_t<T>, detail::dummy>::type>
  43     {
  44         using type = return_type_t<T>;
  45     };
  46 }
  47
  48 //->
  49
  50 template<typename T>
  51 struct return_type : detail::return_type_impl<T> {};
  52
  53 //<-
  54 }} // namespace boost::callable_traits
  55 //->
  56
  57 /*`
  58 [heading Constraints]
  59 * `T` must be one of the following:
  60   * function
  61   * function pointer
  62   * function reference
  63   * member function pointer
  64   * member data pointer
  65   * user-defined type with a non-overloaded `operator()`
  66   * type of a non-generic lambda
  67
  68 [heading Behavior]
  69 * When the constraints are violated, a substitution failure occurs.
  70 * The aliased type is the return type of `T`.
  71
  72 [heading Input/Output Examples]
  73 [table
  74     [[`T`]                              [`return_type_t<T, std::tuple>`]]
  75     [[`void()`]                         [`void`]]
  76     [[`float(*)()`]                     [`float`]]
  77     [[`const char*(&)()`]               [`const char *`]]
  78     [[`int(foo::*)() const`]            [`int`]]
  79     [[`int`]                            [(substitution failure)]]
  80     [[`int (*const)()`]                 [(substitution failure)]]
  81 ]
  82
  83 [heading Example Program]
  84 [import ../example/return_type.cpp]
  85 [return_type]
  86 [endsect]
  87 */
  88 //]
  89
  90 #endif // #ifndef BOOST_CLBL_TRTS_RESULT_OF_HPP