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, c++11, c++14, c++17 10 // UNSUPPORTED: libcpp-no-concepts 11 12 // <bit> 13 // 14 // template<class To, class From> 15 // constexpr To bit_cast(const From& from) noexcept; // C++20 16 17 // This test makes sure that std::bit_cast fails when any of the following 18 // constraints are violated: 19 // 20 // (1.1) sizeof(To) == sizeof(From) is true; 21 // (1.2) is_trivially_copyable_v<To> is true; 22 // (1.3) is_trivially_copyable_v<From> is true. 23 // 24 // Also check that it's ill-formed when the return type would be 25 // ill-formed, even though that is not explicitly mentioned in the 26 // specification (but it can be inferred from the synopsis). 27 28 #include <bit> 29 #include <concepts> 30 31 template<class To, class From> 32 concept bit_cast_is_valid = requires(From from) { 33 { std::bit_cast<To>(from) } -> std::same_as<To>; 34 }; 35 36 // Types are not the same size 37 namespace ns1 { 38 struct To { char a; }; 39 struct From { char a; char b; }; 40 static_assert(!bit_cast_is_valid<To, From>); 41 static_assert(!bit_cast_is_valid<From&, From>); 42 } 43 44 // To is not trivially copyable 45 namespace ns2 { 46 struct To { char a; To(To const&); }; 47 struct From { char a; }; 48 static_assert(!bit_cast_is_valid<To, From>); 49 } 50 51 // From is not trivially copyable 52 namespace ns3 { 53 struct To { char a; }; 54 struct From { char a; From(From const&); }; 55 static_assert(!bit_cast_is_valid<To, From>); 56 } 57 58 // The return type is ill-formed 59 namespace ns4 { 60 struct From { char a; char b; }; 61 static_assert(!bit_cast_is_valid<char[2], From>); 62 static_assert(!bit_cast_is_valid<int(), From>); 63 } 64