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Add
StringRef, BytesRef, and CStringRef to support `std::string…
…_view`
when it is a different type than `absl::string_view`. (Sadly, making
`absl::string_view` convertible from `std::string_view` would lead to
ambiguities e.g. regarding `operator==`.)
`StringRef` stores an `absl::string_view`, possibly converted from
`std::string_view`.
`BytesRef` stores an `absl::string_view`, possibly converted from
`std::string_view` or `absl::Span<const char>`. It replaces
`SupportsToStringView` with `ToStringView()`, but it is a type,
rather than a type predicate associated with a function, and thus
does not require making templates.
`CStringRef` stores a pointer to a C-style NUL-terminated string, or `nullptr`.
The string is copied unless it is known to end with NUL.
They are intended for function parameters when the implementation needs
`absl::string_view` or a C-style NUL-terminated string, and the caller might
have other representations of the string.
Use `CStringRef` in `Owned{Fd,CFile}::Open{,At}()` to reduce the number of
overloads. Also for Windows: while it does not need NUL-termination because
the strings are converted to `std::wstring`, the resulting performance penalty
is dwarfed by the cost of opening the file, and a unified API is nicer.
Make conversions to `absl::string_view` implicit, as is customary.
Make `CompactString` constructible/assignable from and comparable with
`BytesRef` instead of only `absl::string_view`.
Add `CompactString::{at,front,back}()` to complement `operator[]`.
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| Original file line number | Diff line number | Diff line change |
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| // Copyright 2024 Google LLC | ||
| // | ||
| // 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 RIEGELI_BASE_BYTES_REF_H_ | ||
| #define RIEGELI_BASE_BYTES_REF_H_ | ||
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| #include <stddef.h> | ||
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| #include <type_traits> | ||
|
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| #include "absl/base/attributes.h" | ||
| #include "absl/base/config.h" // IWYU pragma: keep | ||
| #include "absl/meta/type_traits.h" | ||
| #include "absl/strings/string_view.h" | ||
| #include "absl/types/span.h" | ||
| #include "riegeli/base/compare.h" | ||
| #include "riegeli/base/string_ref.h" | ||
| #include "riegeli/base/type_traits.h" | ||
|
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| namespace riegeli { | ||
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| // `BytesRef` stores an `absl::string_view` representing text or binary data | ||
| // (see `StringRef` for text data), possibly converted from `std::string_view` | ||
| // or `absl::Span<const char>`. | ||
| // | ||
| // It is intended for function parameters when the implementation needs | ||
| // an `absl::string_view`, and the caller might have another representation | ||
| // of the string. | ||
| // | ||
| // It is convertible from: | ||
| // * types convertible to `absl::string_view` | ||
| // * types convertible to `std::string_view` | ||
| // * types convertible to `absl::Span<const char>`, | ||
| // e.g. `std::vector<char>` or `std::array<char, length>`. | ||
| // | ||
| // `BytesRef` does not own string contents and is efficiently copyable. | ||
| class BytesRef : public StringRef, public WithCompare<BytesRef> { | ||
| public: | ||
| // Stores an empty `absl::string_view`. | ||
| BytesRef() = default; | ||
|
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| // Stores `str` converted to `StringRef` and then to `absl::string_view`. | ||
| template <typename T, | ||
| std::enable_if_t< | ||
| absl::conjunction<NotSelfCopy<BytesRef, T>, | ||
| std::is_convertible<T&&, StringRef>>::value, | ||
| int> = 0> | ||
| /*implicit*/ BytesRef(T&& str ABSL_ATTRIBUTE_LIFETIME_BOUND) | ||
| : StringRef(std::forward<T>(str)) {} | ||
|
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| // Stores `str` converted to `absl::string_view`. | ||
| /*implicit*/ BytesRef( | ||
| absl::Span<const char> str ABSL_ATTRIBUTE_LIFETIME_BOUND) | ||
| : StringRef(absl::string_view(str.data(), str.size())) {} | ||
|
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| // Stores `str` converted to `absl::Span<const char>` and then to | ||
| // `absl::string_view`. | ||
| template <typename T, | ||
| std::enable_if_t< | ||
| absl::conjunction< | ||
| NotSelfCopy<BytesRef, T>, | ||
| absl::negation<std::is_convertible<T&&, StringRef>>, | ||
| absl::negation< | ||
| std::is_same<std::decay_t<T>, absl::Span<const char>>>, | ||
| std::is_convertible<T&&, absl::Span<const char>>>::value, | ||
| int> = 0> | ||
| /*implicit*/ BytesRef(T&& str ABSL_ATTRIBUTE_LIFETIME_BOUND) | ||
| : BytesRef(absl::Span<const char>(std::forward<T>(str))) {} | ||
|
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| BytesRef(const BytesRef& that) = default; | ||
| BytesRef& operator=(const BytesRef&) = delete; | ||
|
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| friend bool operator==(BytesRef a, BytesRef b) { | ||
| return absl::string_view(a) == absl::string_view(b); | ||
| } | ||
| friend riegeli::StrongOrdering RIEGELI_COMPARE(BytesRef a, BytesRef b) { | ||
| return riegeli::Compare(absl::string_view(a), absl::string_view(b)); | ||
| } | ||
|
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| template <typename T, | ||
| std::enable_if_t< | ||
| absl::conjunction<NotSelfCopy<BytesRef, T>, | ||
| std::is_convertible<T&&, StringRef>>::value, | ||
| int> = 0> | ||
| friend bool operator==(BytesRef a, T&& b) { | ||
| return a == BytesRef(std::forward<T>(b)); | ||
| } | ||
| template <typename T, | ||
| std::enable_if_t< | ||
| absl::conjunction<NotSelfCopy<BytesRef, T>, | ||
| std::is_convertible<T&&, StringRef>>::value, | ||
| int> = 0> | ||
| friend riegeli::StrongOrdering RIEGELI_COMPARE(BytesRef a, T&& b) { | ||
| return riegeli::Compare(a, BytesRef(std::forward<T>(b))); | ||
| } | ||
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| // `absl::Span<const char>` is already comparable against types convertible to | ||
| // `absl::Span<const char>`, which includes `BytesRef`. | ||
| }; | ||
|
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| } // namespace riegeli | ||
|
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| #endif // RIEGELI_BASE_BYTES_REF_H_ |
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