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author | 2017-09-19 16:54:40 -0400 | |
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committer | 2017-09-19 16:54:40 -0400 | |
commit | c2e754829628d1e9b7a16b3389cfdace76950fdf (patch) | |
tree | 5a7f056f44e27c30e10025113b644f0b3b5801fc /absl/strings/internal/resize_uninitialized.h |
Initial Commit
Diffstat (limited to 'absl/strings/internal/resize_uninitialized.h')
-rw-r--r-- | absl/strings/internal/resize_uninitialized.h | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/absl/strings/internal/resize_uninitialized.h b/absl/strings/internal/resize_uninitialized.h new file mode 100644 index 00000000..0157ca02 --- /dev/null +++ b/absl/strings/internal/resize_uninitialized.h @@ -0,0 +1,69 @@ +// +// 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 +// +// http://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 <utility> + +#include "absl/base/port.h" +#include "absl/meta/type_traits.h" // for void_t + +namespace absl { +namespace strings_internal { + +// Is a subclass of true_type or false_type, depending on whether or not +// T has a resize_uninitialized member. +template <typename T, typename = void> +struct HasResizeUninitialized : std::false_type {}; +template <typename T> +struct HasResizeUninitialized< + T, absl::void_t<decltype(std::declval<T>().resize_uninitialized(237))>> + : std::true_type {}; + +template <typename string_type> +void ResizeUninit(string_type* s, size_t new_size, std::true_type) { + s->resize_uninitialized(new_size); +} +template <typename string_type> +void ResizeUninit(string_type* s, size_t new_size, std::false_type) { + s->resize(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 HasResizeUninitialized<string_type>(); +} + +// 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. Uses a Google extension to std::string. +template <typename string_type, typename = void> +inline void STLStringResizeUninitialized(string_type* s, size_t new_size) { + ResizeUninit(s, new_size, HasResizeUninitialized<string_type>()); +} + +} // namespace strings_internal +} // namespace absl + +#endif // ABSL_STRINGS_INTERNAL_RESIZE_UNINITIALIZED_H_ |