1 // Copyright 2023 The Pigweed Authors
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License"); you may not
4 // use this file except in compliance with the License. You may obtain a copy of
5 // the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
11 // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12 // License for the specific language governing permissions and limitations under
13 // the License.
14 #pragma once
15
16 #include <cstddef>
17
18 #include "pw_polyfill/language_feature_macros.h"
19
20 namespace pw {
21 namespace internal {
22
23 // This function is not intended for use by end-users.
24 //
25 // This function does nothing, but attempting to call it in a constexpr
26 // context will result in a compilation error.
27 //
28 // If it appears in an error like the following:
29 //
30 // ```
31 // error: call to consteval function 'pw::operator""_b' is not a constant
32 // expression
33 // ...
34 // note: non-constexpr function 'ByteLiteralIsTooLarge' cannot be used in a
35 // constant expression
36 // ```
37 //
38 // Then a byte-literal with a value exceeding 255 has been written.
39 // For example, ``255_b`` is okay, but ``256_b`` will result in an error.
ByteLiteralIsTooLarge()40 inline void ByteLiteralIsTooLarge() {}
41
42 } // namespace internal
43
44 /// Returns a ``std::byte`` when used as a ``_b`` suffix.
45 ///
46 /// This is useful for writing byte literals, particularly in tests.
47 /// To use, add ``using ::pw::operator""_b;`` and then use like ``5_b``
48 /// in order to create a ``std::byte`` with the contents ``5``.
49 ///
50 /// This should not be used in header files, as it requires a ``using``
51 /// declaration that will be publicly exported at whatever level it is
52 /// used.
53 PW_CONSTEVAL std::byte operator""_b(unsigned long long value) {
54 if (value > 255) {
55 internal::ByteLiteralIsTooLarge();
56 }
57 return std::byte(value);
58 }
59
60 } // namespace pw
61