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 11 // <bit> 12 // 13 // template<class To, class From> 14 // constexpr To bit_cast(const From& from) noexcept; // C++20 15 16 // This test makes sure that std::bit_cast fails when any of the following 17 // constraints are violated: 18 // 19 // (1.1) sizeof(To) == sizeof(From) is true; 20 // (1.2) is_trivially_copyable_v<To> is true; 21 // (1.3) is_trivially_copyable_v<From> is true. 22 // 23 // Also check that it's ill-formed when the return type would be 24 // ill-formed, even though that is not explicitly mentioned in the 25 // specification (but it can be inferred from the synopsis). 26 27 #include <bit> 28 #include <concepts> 29 30 template<class To, class From> 31 concept bit_cast_is_valid = requires(From from) { 32 { std::bit_cast<To>(from) } -> std::same_as<To>; 33 }; 34 35 // Types are not the same size 36 namespace ns1 { 37 struct To { char a; }; 38 struct From { char a; char b; }; 39 static_assert(!bit_cast_is_valid<To, From>); 40 static_assert(!bit_cast_is_valid<From&, From>); 41 } 42 43 // To is not trivially copyable 44 namespace ns2 { 45 struct To { char a; To(To const&); }; 46 struct From { char a; }; 47 static_assert(!bit_cast_is_valid<To, From>); 48 } 49 50 // From is not trivially copyable 51 namespace ns3 { 52 struct To { char a; }; 53 struct From { char a; From(From const&); }; 54 static_assert(!bit_cast_is_valid<To, From>); 55 } 56 57 // The return type is ill-formed 58 namespace ns4 { 59 struct From { char a; char b; }; 60 static_assert(!bit_cast_is_valid<char[2], From>); 61 static_assert(!bit_cast_is_valid<int(), From>); 62 } 63