| // Copyright 2022 The Abseil Authors | |
| // | |
| // Licensed under the Apache License, Version 2.0 (the "License"); | |
| // you may not use this file except in compliance with the License. | |
| // You may obtain a copy of the License at | |
| // | |
| // https://www.apache.org/licenses/LICENSE-2.0 | |
| // | |
| // Unless required by applicable law or agreed to in writing, software | |
| // distributed under the License is distributed on an "AS IS" BASIS, | |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
| // See the License for the specific language governing permissions and | |
| // limitations under the License. | |
| namespace absl { | |
| ABSL_NAMESPACE_BEGIN | |
| namespace strings_internal { | |
| // This is an empty class not intended to be used. It exists so that | |
| // `HasAbslStringify` can reference a universal class rather than needing to be | |
| // copied for each new sink. | |
| class UnimplementedSink { | |
| public: | |
| void Append(size_t count, char ch); | |
| void Append(string_view v); | |
| // Support `absl::Format(&sink, format, args...)`. | |
| friend void AbslFormatFlush(UnimplementedSink* sink, absl::string_view v); | |
| }; | |
| } // namespace strings_internal | |
| // `HasAbslStringify<T>` detects if type `T` supports the `AbslStringify()` | |
| // customization point (see | |
| // https://abseil.io/docs/cpp/guides/format#abslstringify for the | |
| // documentation). | |
| // | |
| // Note that there are types that can be `StrCat`-ed that do not use the | |
| // `AbslStringify` customization point (for example, `int`). | |
| template <typename T, typename = void> | |
| struct HasAbslStringify : std::false_type {}; | |
| template <typename T> | |
| struct HasAbslStringify< | |
| T, std::enable_if_t<std::is_void<decltype(AbslStringify( | |
| std::declval<strings_internal::UnimplementedSink&>(), | |
| std::declval<const T&>()))>::value>> : std::true_type {}; | |
| ABSL_NAMESPACE_END | |
| } // namespace absl | |