libcxx/test/std/utilities/utility/forward/forward.pass.cpp

   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 // UNSUPPORTED: c++03
  10
  11 // test forward
  12
  13 #include <utility>
  14 #include <type_traits>
  15 #include <cassert>
  16
  17 #include "test_macros.h"
  18
  19 struct A
  20 {
  21 };
  22
  23 A source() TEST_NOEXCEPT {return A();}
  24 const A csource() TEST_NOEXCEPT {return A();}
  25
  26
  27 #if TEST_STD_VER > 11
  28 constexpr bool test_constexpr_forward() {
  29     int x = 42;
  30     const int cx = 101;
  31     return std::forward<int&>(x)        == 42
  32         && std::forward<int>(x)         == 42
  33         && std::forward<const int&>(x)  == 42
  34         && std::forward<const int>(x)   == 42
  35         && std::forward<int&&>(x)       == 42
  36         && std::forward<const int&&>(x) == 42
  37         && std::forward<const int&>(cx) == 101
  38         && std::forward<const int>(cx)  == 101;
  39 }
  40 #endif
  41
  42 int main(int, char**)
  43 {
  44     A a;
  45     const A ca = A();
  46
  47     ((void)a); // Prevent unused warning
  48     ((void)ca); // Prevent unused warning
  49
  50     static_assert(std::is_same<decltype(std::forward<A&>(a)), A&>::value, "");
  51     static_assert(std::is_same<decltype(std::forward<A>(a)), A&&>::value, "");
  52     static_assert(std::is_same<decltype(std::forward<A>(source())), A&&>::value, "");
  53     ASSERT_NOEXCEPT(std::forward<A&>(a));
  54     ASSERT_NOEXCEPT(std::forward<A>(a));
  55     ASSERT_NOEXCEPT(std::forward<A>(source()));
  56
  57     static_assert(std::is_same<decltype(std::forward<const A&>(a)), const A&>::value, "");
  58     static_assert(std::is_same<decltype(std::forward<const A>(a)), const A&&>::value, "");
  59     static_assert(std::is_same<decltype(std::forward<const A>(source())), const A&&>::value, "");
  60     ASSERT_NOEXCEPT(std::forward<const A&>(a));
  61     ASSERT_NOEXCEPT(std::forward<const A>(a));
  62     ASSERT_NOEXCEPT(std::forward<const A>(source()));
  63
  64     static_assert(std::is_same<decltype(std::forward<const A&>(ca)), const A&>::value, "");
  65     static_assert(std::is_same<decltype(std::forward<const A>(ca)), const A&&>::value, "");
  66     static_assert(std::is_same<decltype(std::forward<const A>(csource())), const A&&>::value, "");
  67     ASSERT_NOEXCEPT(std::forward<const A&>(ca));
  68     ASSERT_NOEXCEPT(std::forward<const A>(ca));
  69     ASSERT_NOEXCEPT(std::forward<const A>(csource()));
  70
  71 #if TEST_STD_VER > 11
  72     {
  73     constexpr int i2 = std::forward<int>(42);
  74     static_assert(std::forward<int>(42) == 42, "");
  75     static_assert(std::forward<const int&>(i2) == 42, "");
  76     static_assert(test_constexpr_forward(), "");
  77     }
  78 #endif
  79 #if TEST_STD_VER == 11 && defined(_LIBCPP_VERSION)
  80     // Test that std::forward is constexpr in C++11. This is an extension
  81     // provided by both libc++ and libstdc++.
  82     {
  83     constexpr int i2 = std::forward<int>(42);
  84     static_assert(std::forward<int>(42) == 42, "" );
  85     static_assert(std::forward<const int&>(i2) == 42, "");
  86     }
  87 #endif
  88
  89   return 0;
  90 }