libcxx/test/support/test_convertible.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef SUPPORT_TEST_CONVERTIBLE_H
  10 #define SUPPORT_TEST_CONVERTIBLE_H
  11
  12 // "test_convertible<Tp, Args...>()" is a metafunction used to check if 'Tp'
  13 // is implicitly convertible from 'Args...' for any number of arguments,
  14 // Unlike 'std::is_convertible' which only allows checking for single argument
  15 // conversions.
  16
  17 #include <type_traits>
  18
  19 #include "test_macros.h"
  20
  21 #if TEST_STD_VER < 11
  22 #error test_convertible.h requires C++11 or newer
  23 #endif
  24
  25 namespace detail {
  26     template <class Tp> void eat_type(Tp);
  27
  28     template <class Tp, class ...Args>
  29     constexpr auto test_convertible_imp(int)
  30         -> decltype(eat_type<Tp>({std::declval<Args>()...}), true)
  31     { return true; }
  32
  33     template <class Tp, class ...Args>
  34     constexpr auto test_convertible_imp(long) -> bool { return false; }
  35 }
  36
  37 template <class Tp, class ...Args>
  38 constexpr bool test_convertible()
  39 { return detail::test_convertible_imp<Tp, Args...>(0); }
  40
  41 #endif // SUPPORT_TEST_CONVERTIBLE_H