| // 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. |
| |
| #ifndef ABSL_STRINGS_HAS_ABSL_STRINGIFY_H_ |
| #define ABSL_STRINGS_HAS_ABSL_STRINGIFY_H_ |
| |
| #include <type_traits> |
| #include <utility> |
| |
| #include "absl/strings/string_view.h" |
| |
| 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 |
| |
| #endif // ABSL_STRINGS_HAS_ABSL_STRINGIFY_H_ |