diff options
Diffstat (limited to 'third_party/abseil_cpp/absl/strings/internal/resize_uninitialized.h')
-rw-r--r-- | third_party/abseil_cpp/absl/strings/internal/resize_uninitialized.h | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/third_party/abseil_cpp/absl/strings/internal/resize_uninitialized.h b/third_party/abseil_cpp/absl/strings/internal/resize_uninitialized.h new file mode 100644 index 000000000000..e42628e3949a --- /dev/null +++ b/third_party/abseil_cpp/absl/strings/internal/resize_uninitialized.h @@ -0,0 +1,73 @@ +// +// Copyright 2017 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_INTERNAL_RESIZE_UNINITIALIZED_H_ +#define ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_ + +#include <string> +#include <type_traits> +#include <utility> + +#include "absl/base/port.h" +#include "absl/meta/type_traits.h" // for void_t + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace strings_internal { + +// Is a subclass of true_type or false_type, depending on whether or not +// T has a __resize_default_init member. +template <typename string_type, typename = void> +struct ResizeUninitializedTraits { + using HasMember = std::false_type; + static void Resize(string_type* s, size_t new_size) { s->resize(new_size); } +}; + +// __resize_default_init is provided by libc++ >= 8.0 +template <typename string_type> +struct ResizeUninitializedTraits< + string_type, absl::void_t<decltype(std::declval<string_type&>() + .__resize_default_init(237))> > { + using HasMember = std::true_type; + static void Resize(string_type* s, size_t new_size) { + s->__resize_default_init(new_size); + } +}; + +// Returns true if the std::string implementation supports a resize where +// the new characters added to the std::string are left untouched. +// +// (A better name might be "STLStringSupportsUninitializedResize", alluding to +// the previous function.) +template <typename string_type> +inline constexpr bool STLStringSupportsNontrashingResize(string_type*) { + return ResizeUninitializedTraits<string_type>::HasMember::value; +} + +// Like str->resize(new_size), except any new characters added to "*str" as a +// result of resizing may be left uninitialized, rather than being filled with +// '0' bytes. Typically used when code is then going to overwrite the backing +// store of the std::string with known data. +template <typename string_type, typename = void> +inline void STLStringResizeUninitialized(string_type* s, size_t new_size) { + ResizeUninitializedTraits<string_type>::Resize(s, new_size); +} + +} // namespace strings_internal +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_ |