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Diffstat (limited to 'absl/strings/cord.h')
| -rw-r--r-- | absl/strings/cord.h | 638 |
1 files changed, 442 insertions, 196 deletions
diff --git a/absl/strings/cord.h b/absl/strings/cord.h index 66645eef6e48..3ab3cb87f520 100644 --- a/absl/strings/cord.h +++ b/absl/strings/cord.h @@ -11,25 +11,52 @@ // 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. - -// A Cord is a sequence of characters with some unusual access propreties. -// A Cord supports efficient insertions and deletions at the start and end of -// the byte sequence, but random access reads are slower, and random access -// modifications are not supported by the API. Cord also provides cheap copies -// (using a copy-on-write strategy) and cheap substring operations. // -// Thread safety -// ------------- +// ----------------------------------------------------------------------------- +// File: cord.h +// ----------------------------------------------------------------------------- +// +// This file defines the `absl::Cord` data structure and operations on that data +// structure. A Cord is a string-like sequence of characters optimized for +// specific use cases. Unlike a `std::string`, which stores an array of +// contiguous characters, Cord data is stored in a structure consisting of +// separate, reference-counted "chunks." (Currently, this implementation is a +// tree structure, though that implementation may change.) +// +// Because a Cord consists of these chunks, data can be added to or removed from +// a Cord during its lifetime. Chunks may also be shared between Cords. Unlike a +// `std::string`, a Cord can therefore accomodate data that changes over its +// lifetime, though it's not quite "mutable"; it can change only in the +// attachment, detachment, or rearrangement of chunks of its constituent data. +// +// A Cord provides some benefit over `std::string` under the following (albeit +// narrow) circumstances: +// +// * Cord data is designed to grow and shrink over a Cord's lifetime. Cord +// provides efficient insertions and deletions at the start and end of the +// character sequences, avoiding copies in those cases. Static data should +// generally be stored as strings. +// * External memory consisting of string-like data can be directly added to +// a Cord without requiring copies or allocations. +// * Cord data may be shared and copied cheaply. Cord provides a copy-on-write +// implementation and cheap sub-Cord operations. Copying a Cord is an O(1) +// operation. +// +// As a consequence to the above, Cord data is generally large. Small data +// should generally use strings, as construction of a Cord requires some +// overhead. Small Cords (<= 15 bytes) are represented inline, but most small +// Cords are expected to grow over their lifetimes. +// +// Note that because a Cord is made up of separate chunked data, random access +// to character data within a Cord is slower than within a `std::string`. +// +// Thread Safety +// // Cord has the same thread-safety properties as many other types like // std::string, std::vector<>, int, etc -- it is thread-compatible. In -// particular, if no thread may call a non-const method, then it is safe to -// concurrently call const methods. Copying a Cord produces a new instance that -// can be used concurrently with the original in arbitrary ways. -// -// Implementation is similar to the "Ropes" described in: -// Ropes: An alternative to strings -// Hans J. Boehm, Russ Atkinson, Michael Plass -// Software Practice and Experience, December 1995 +// particular, if threads do not call non-const methods, then it is safe to call +// const methods without synchronization. Copying a Cord produces a new instance +// that can be used concurrently with the original in arbitrary ways. #ifndef ABSL_STRINGS_CORD_H_ #define ABSL_STRINGS_CORD_H_ @@ -68,6 +95,90 @@ template <typename H> H HashFragmentedCord(H, const Cord&); } +// Cord +// +// A Cord is a sequence of characters, designed to be more efficient than a +// `std::string` in certain circumstances: namely, large string data that needs +// to change over its lifetime or shared, especially when such data is shared +// across API boundaries. +// +// A Cord stores its character data in a structure that allows efficient prepend +// and append operations. This makes a Cord useful for large string data sent +// over in a wire format that may need to be prepended or appended at some point +// during the data exchange (e.g. HTTP, protocol buffers). For example, a +// Cord is useful for storing an HTTP request, and prepending an HTTP header to +// such a request. +// +// Cords should not be used for storing general string data, however. They +// require overhead to construct and are slower than strings for random access. +// +// The Cord API provides the following common API operations: +// +// * Create or assign Cords out of existing string data, memory, or other Cords +// * Append and prepend data to an existing Cord +// * Create new Sub-Cords from existing Cord data +// * Swap Cord data and compare Cord equality +// * Write out Cord data by constructing a `std::string` +// +// Additionally, the API provides iterator utilities to iterate through Cord +// data via chunks or character bytes. +// + +namespace cord_internal { + +// It's expensive to keep a Cord's tree perfectly balanced, so instead we keep +// trees approximately balanced. A tree node N of depth D(N) that contains a +// string of L(N) characters is considered balanced if L >= Fibonacci(D + 2). +// The "+ 2" is used to ensure that every balanced leaf node contains at least +// one character. Here we presume that +// Fibonacci(0) = 0 +// Fibonacci(1) = 1 +// Fibonacci(2) = 1 +// Fibonacci(3) = 2 +// ... +// The algorithm is based on paper by Hans Boehm et al: +// https://www.cs.rit.edu/usr/local/pub/jeh/courses/QUARTERS/FP/Labs/CedarRope/rope-paper.pdf +// In this paper authors shows that rebalancing based on cord forest of already +// balanced subtrees can be proven to never produce tree of depth larger than +// largest Fibonacci number representable in the same integral type as cord size +// For 64 bit integers this is the 93rd Fibonacci number. For 32 bit integrals +// this is 47th Fibonacci number. +constexpr size_t MaxCordDepth() { return sizeof(size_t) == 8 ? 93 : 47; } + +// This class models fixed max size stack of CordRep pointers. +// The elements are being pushed back and popped from the back. +template <typename CordRepPtr, size_t N> +class CordTreePath { + public: + CordTreePath() {} + explicit CordTreePath(CordRepPtr root) { push_back(root); } + + bool empty() const { return size_ == 0; } + size_t size() const { return size_; } + void clear() { size_ = 0; } + + CordRepPtr back() { return data_[size_ - 1]; } + + void pop_back() { + --size_; + assert(size_ < N); + } + void push_back(CordRepPtr elem) { data_[size_++] = elem; } + + private: + CordRepPtr data_[N]; + size_t size_ = 0; +}; + +// Fixed length container for mutable "path" in cord tree, which can hold any +// possible valid path in cord tree. +using CordTreeMutablePath = CordTreePath<CordRep*, MaxCordDepth()>; +// Variable length container for mutable "path" in cord tree. It starts with +// capacity for 15 elements and grow if necessary. +using CordTreeDynamicPath = + absl::InlinedVector<absl::cord_internal::CordRep*, 15>; +} // namespace cord_internal + // A Cord is a sequence of characters. class Cord { private: @@ -75,53 +186,124 @@ class Cord { using EnableIfString = absl::enable_if_t<std::is_same<T, std::string>::value, int>; + //---------------------------------------------------------------------------- + // Cord::GenericChunkIterator + //---------------------------------------------------------------------------- + // + // A `Cord::GenericChunkIterator` provides an interface for the standard + // `Cord::ChunkIterator` as well as some private implementations. + template <typename StorageType> + class GenericChunkIterator { + public: + using iterator_category = std::input_iterator_tag; + using value_type = absl::string_view; + using difference_type = ptrdiff_t; + using pointer = const value_type*; + using reference = value_type; + + GenericChunkIterator() = default; + + GenericChunkIterator& operator++(); + GenericChunkIterator operator++(int); + bool operator==(const GenericChunkIterator& other) const; + bool operator!=(const GenericChunkIterator& other) const; + reference operator*() const; + pointer operator->() const; + + friend class Cord; + friend class CharIterator; + + private: + // Constructs a `begin()` iterator from `cord`. + explicit GenericChunkIterator(const Cord* cord); + + // Removes `n` bytes from `current_chunk_`. Expects `n` to be smaller than + // `current_chunk_.size()`. + void RemoveChunkPrefix(size_t n); + Cord AdvanceAndReadBytes(size_t n); + void AdvanceBytes(size_t n); + // Iterates `n` bytes, where `n` is expected to be greater than or equal to + // `current_chunk_.size()`. + void AdvanceBytesSlowPath(size_t n); + + // A view into bytes of the current `CordRep`. It may only be a view to a + // suffix of bytes if this is being used by `CharIterator`. + absl::string_view current_chunk_; + // The current leaf, or `nullptr` if the iterator points to short data. + // If the current chunk is a substring node, current_leaf_ points to the + // underlying flat or external node. + cord_internal::CordRep* current_leaf_ = nullptr; + // The number of bytes left in the `Cord` over which we are iterating. + size_t bytes_remaining_ = 0; + StorageType stack_of_right_children_; + }; + template <typename IteratorType> + class GenericChunkRange { + public: + explicit GenericChunkRange(const Cord* cord) : cord_(cord) {} + + IteratorType begin() const { return IteratorType(cord_); } + IteratorType end() const { return IteratorType(); } + + private: + const Cord* cord_; + }; + public: - // -------------------------------------------------------------------- - // Constructors, destructors and helper factories + // Cord::Cord() Constructors - // Create an empty cord + // Creates an empty Cord constexpr Cord() noexcept; - // Cord is copyable and efficiently movable. - // The moved-from state is valid but unspecified. + // Creates a Cord from an existing Cord. Cord is copyable and efficiently + // movable. The moved-from state is valid but unspecified. Cord(const Cord& src); Cord(Cord&& src) noexcept; Cord& operator=(const Cord& x); Cord& operator=(Cord&& x) noexcept; - // Create a cord out of "src". This constructor is explicit on - // purpose so that people do not get automatic type conversions. + // Creates a Cord from a `src` string. This constructor is marked explicit to + // prevent implicit Cord constructions from arguments convertible to an + // `absl::string_view`. explicit Cord(absl::string_view src); Cord& operator=(absl::string_view src); - // These are templated to avoid ambiguities for types that are convertible to - // both `absl::string_view` and `std::string`, such as `const char*`. + // Creates a Cord from a `std::string&&` rvalue. These constructors are + // templated to avoid ambiguities for types that are convertible to both + // `absl::string_view` and `std::string`, such as `const char*`. // - // Note that these functions reserve the right to reuse the `string&&`'s + // Note that these functions reserve the right to use the `string&&`'s // memory and that they will do so in the future. template <typename T, EnableIfString<T> = 0> explicit Cord(T&& src) : Cord(absl::string_view(src)) {} template <typename T, EnableIfString<T> = 0> Cord& operator=(T&& src); - // Destroy the cord + // Cord::~Cord() + // + // Destructs the Cord ~Cord() { if (contents_.is_tree()) DestroyCordSlow(); } - // Creates a Cord that takes ownership of external memory. The contents of - // `data` are not copied. + // Cord::MakeCordFromExternal(data, callable) + // + // Creates a Cord that takes ownership of external string memory. The + // contents of `data` are not copied to the Cord; instead, the external + // memory is added to the Cord and reference-counted. This data may not be + // changed for the life of the Cord, though it may be prepended or appended + // to. + // + // `MakeCordFromExternal()` takes a callable "releaser" that is invoked when + // the reference count for `data` reaches zero. As noted above, this data must + // remain live until the releaser is invoked. The callable releaser also must: // - // This function takes a callable that is invoked when all Cords are - // finished with `data`. The data must remain live and unchanging until the - // releaser is called. The requirements for the releaser are that it: - // * is move constructible, - // * supports `void operator()(absl::string_view) const` or - // `void operator()() const`, - // * does not have alignment requirement greater than what is guaranteed by - // ::operator new. This is dictated by alignof(std::max_align_t) before - // C++17 and __STDCPP_DEFAULT_NEW_ALIGNMENT__ if compiling with C++17 or - // it is supported by the implementation. + // * be move constructible + // * support `void operator()(absl::string_view) const` or `void operator()` + // * not have alignment requirement greater than what is guaranteed by + // `::operator new`. This alignment is dictated by + // `alignof(std::max_align_t)` (pre-C++17 code) or + // `__STDCPP_DEFAULT_NEW_ALIGNMENT__` (C++17 code). // // Example: // @@ -135,8 +317,8 @@ class Cord { // }); // } // - // WARNING: It's likely a bug if your releaser doesn't do anything. - // For example, consider the following: + // WARNING: Because a Cord can be reference-counted, it's likely a bug if your + // releaser doesn't do anything. For example, consider the following: // // void Foo(const char* buffer, int len) { // auto c = absl::MakeCordFromExternal(absl::string_view(buffer, len), @@ -150,67 +332,100 @@ class Cord { template <typename Releaser> friend Cord MakeCordFromExternal(absl::string_view data, Releaser&& releaser); - // -------------------------------------------------------------------- - // Mutations - + // Cord::Clear() + // + // Releases the Cord data. Any nodes that share data with other Cords, if + // applicable, will have their reference counts reduced by 1. void Clear(); + // Cord::Append() + // + // Appends data to the Cord, which may come from another Cord or other string + // data. void Append(const Cord& src); void Append(Cord&& src); void Append(absl::string_view src); template <typename T, EnableIfString<T> = 0> void Append(T&& src); + // Cord::Prepend() + // + // Prepends data to the Cord, which may come from another Cord or other string + // data. void Prepend(const Cord& src); void Prepend(absl::string_view src); template <typename T, EnableIfString<T> = 0> void Prepend(T&& src); + // Cord::RemovePrefix() + // + // Removes the first `n` bytes of a Cord. void RemovePrefix(size_t n); void RemoveSuffix(size_t n); - // Returns a new cord representing the subrange [pos, pos + new_size) of + // Cord::Subcord() + // + // Returns a new Cord representing the subrange [pos, pos + new_size) of // *this. If pos >= size(), the result is empty(). If // (pos + new_size) >= size(), the result is the subrange [pos, size()). Cord Subcord(size_t pos, size_t new_size) const; + // swap() + // + // Swaps the data of Cord `x` with Cord `y`. friend void swap(Cord& x, Cord& y) noexcept; - // -------------------------------------------------------------------- - // Accessors - + // Cord::size() + // + // Returns the size of the Cord. size_t size() const; + + // Cord::empty() + // + // Determines whether the given Cord is empty, returning `true` is so. bool empty() const; - // Returns the approximate number of bytes pinned by this Cord. Note that - // Cords that share memory could each be "charged" independently for the same - // shared memory. + // Cord:EstimatedMemoryUsage() + // + // Returns the *approximate* number of bytes held in full or in part by this + // Cord (which may not remain the same between invocations). Note that Cords + // that share memory could each be "charged" independently for the same shared + // memory. size_t EstimatedMemoryUsage() const; - // -------------------------------------------------------------------- - // Comparators - - // Compares 'this' Cord with rhs. This function and its relatives - // treat Cords as sequences of unsigned bytes. The comparison is a - // straightforward lexicographic comparison. Return value: + // Cord::Compare() + // + // Compares 'this' Cord with rhs. This function and its relatives treat Cords + // as sequences of unsigned bytes. The comparison is a straightforward + // lexicographic comparison. `Cord::Compare()` returns values as follows: + // // -1 'this' Cord is smaller // 0 two Cords are equal // 1 'this' Cord is larger int Compare(absl::string_view rhs) const; int Compare(const Cord& rhs) const; - // Does 'this' cord start/end with rhs + // Cord::StartsWith() + // + // Determines whether the Cord starts with the passed string data `rhs`. bool StartsWith(const Cord& rhs) const; bool StartsWith(absl::string_view rhs) const; + + // Cord::EndsWidth() + // + // Determines whether the Cord ends with the passed string data `rhs`. bool EndsWith(absl::string_view rhs) const; bool EndsWith(const Cord& rhs) const; - // -------------------------------------------------------------------- - // Conversion to other types - + // Cord::operator std::string() + // + // Converts a Cord into a `std::string()`. This operator is marked explicit to + // prevent unintended Cord usage in functions that take a string. explicit operator std::string() const; - // Copies the contents from `src` to `*dst`. + // CopyCordToString() + // + // Copies the contents of a `src` Cord into a `*dst` string. // // This function optimizes the case of reusing the destination string since it // can reuse previously allocated capacity. However, this function does not @@ -219,80 +434,46 @@ class Cord { // object, prefer to simply use the conversion operator to `std::string`. friend void CopyCordToString(const Cord& src, std::string* dst); - // -------------------------------------------------------------------- - // Iteration - class CharIterator; - // Type for iterating over the chunks of a `Cord`. See comments for - // `Cord::chunk_begin()`, `Cord::chunk_end()` and `Cord::Chunks()` below for - // preferred usage. + //---------------------------------------------------------------------------- + // Cord::ChunkIterator + //---------------------------------------------------------------------------- + // + // A `Cord::ChunkIterator` allows iteration over the constituent chunks of its + // Cord. Such iteration allows you to perform non-const operatons on the data + // of a Cord without modifying it. + // + // Generally, you do not instantiate a `Cord::ChunkIterator` directly; + // instead, you create one implicitly through use of the `Cord::Chunks()` + // member function. // - // Additional notes: + // The `Cord::ChunkIterator` has the following properties: + // + // * The iterator is invalidated after any non-const operation on the + // Cord object over which it iterates. // * The `string_view` returned by dereferencing a valid, non-`end()` // iterator is guaranteed to be non-empty. - // * A `ChunkIterator` object is invalidated after any non-const - // operation on the `Cord` object over which it iterates. - // * Two `ChunkIterator` objects can be equality compared if and only if - // they remain valid and iterate over the same `Cord`. - // * This is a proxy iterator. This means the `string_view` returned by the - // iterator does not live inside the Cord, and its lifetime is limited to - // the lifetime of the iterator itself. To help prevent issues, - // `ChunkIterator::reference` is not a true reference type and is - // equivalent to `value_type`. - // * The iterator keeps state that can grow for `Cord`s that contain many + // * Two `ChunkIterator` objects can be compared equal if and only if they + // remain valid and iterate over the same Cord. + // * The iterator in this case is a proxy iterator; the `string_view` + // returned by the iterator does not live inside the Cord, and its + // lifetime is limited to the lifetime of the iterator itself. To help + // prevent lifetime issues, `ChunkIterator::reference` is not a true + // reference type and is equivalent to `value_type`. + // * The iterator keeps state that can grow for Cords that contain many // nodes and are imbalanced due to sharing. Prefer to pass this type by // const reference instead of by value. - class ChunkIterator { - public: - using iterator_category = std::input_iterator_tag; - using value_type = absl::string_view; - using difference_type = ptrdiff_t; - using pointer = const value_type*; - using reference = value_type; - - ChunkIterator() = default; - - ChunkIterator& operator++(); - ChunkIterator operator++(int); - bool operator==(const ChunkIterator& other) const; - bool operator!=(const ChunkIterator& other) const; - reference operator*() const; - pointer operator->() const; - - friend class Cord; - friend class CharIterator; - - private: - // Constructs a `begin()` iterator from `cord`. - explicit ChunkIterator(const Cord* cord); - - // Removes `n` bytes from `current_chunk_`. Expects `n` to be smaller than - // `current_chunk_.size()`. - void RemoveChunkPrefix(size_t n); - Cord AdvanceAndReadBytes(size_t n); - void AdvanceBytes(size_t n); - // Iterates `n` bytes, where `n` is expected to be greater than or equal to - // `current_chunk_.size()`. - void AdvanceBytesSlowPath(size_t n); - - // A view into bytes of the current `CordRep`. It may only be a view to a - // suffix of bytes if this is being used by `CharIterator`. - absl::string_view current_chunk_; - // The current leaf, or `nullptr` if the iterator points to short data. - // If the current chunk is a substring node, current_leaf_ points to the - // underlying flat or external node. - absl::cord_internal::CordRep* current_leaf_ = nullptr; - // The number of bytes left in the `Cord` over which we are iterating. - size_t bytes_remaining_ = 0; - absl::InlinedVector<absl::cord_internal::CordRep*, 4> - stack_of_right_children_; - }; + using ChunkIterator = + GenericChunkIterator<cord_internal::CordTreeDynamicPath>; + // Cord::ChunkIterator::chunk_begin() + // // Returns an iterator to the first chunk of the `Cord`. // - // This is useful for getting a `ChunkIterator` outside the context of a - // range-based for-loop (in which case see `Cord::Chunks()` below). + // Generally, prefer using `Cord::Chunks()` within a range-based for loop for + // iterating over the chunks of a Cord. This method may be useful for getting + // a `ChunkIterator` where range-based for-loops are not useful. // // Example: // @@ -301,26 +482,35 @@ class Cord { // return std::find(c.chunk_begin(), c.chunk_end(), s); // } ChunkIterator chunk_begin() const; + + // Cord::ChunkItertator::chunk_end() + // // Returns an iterator one increment past the last chunk of the `Cord`. + // + // Generally, prefer using `Cord::Chunks()` within a range-based for loop for + // iterating over the chunks of a Cord. This method may be useful for getting + // a `ChunkIterator` where range-based for-loops may not be available. ChunkIterator chunk_end() const; - // Convenience wrapper over `Cord::chunk_begin()` and `Cord::chunk_end()` to - // enable range-based for-loop iteration over `Cord` chunks. + //---------------------------------------------------------------------------- + // Cord::ChunkIterator::ChunkRange + //---------------------------------------------------------------------------- // - // Prefer to use `Cord::Chunks()` below instead of constructing this directly. - class ChunkRange { - public: - explicit ChunkRange(const Cord* cord) : cord_(cord) {} - - ChunkIterator begin() const; - ChunkIterator end() const; - - private: - const Cord* cord_; - }; + // `ChunkRange` is a helper class for iterating over the chunks of the `Cord`, + // producing an iterator which can be used within a range-based for loop. + // Construction of a `ChunkRange` will return an iterator pointing to the + // first chunk of the Cord. Generally, do not construct a `ChunkRange` + // directly; instead, prefer to use the `Cord::Chunks()` method. + // + // Implementation note: `ChunkRange` is simply a convenience wrapper over + // `Cord::chunk_begin()` and `Cord::chunk_end()`. + using ChunkRange = GenericChunkRange<ChunkIterator>; - // Returns a range for iterating over the chunks of a `Cord` with a - // range-based for-loop. + // Cord::Chunks() + // + // Returns a `Cord::ChunkIterator::ChunkRange` for iterating over the chunks + // of a `Cord` with a range-based for-loop. For most iteration tasks on a + // Cord, use `Cord::Chunks()` to retrieve this iterator. // // Example: // @@ -337,22 +527,30 @@ class Cord { // } ChunkRange Chunks() const; - // Type for iterating over the characters of a `Cord`. See comments for - // `Cord::char_begin()`, `Cord::char_end()` and `Cord::Chars()` below for - // preferred usage. + //---------------------------------------------------------------------------- + // Cord::CharIterator + //---------------------------------------------------------------------------- + // + // A `Cord::CharIterator` allows iteration over the constituent characters of + // a `Cord`. + // + // Generally, you do not instantiate a `Cord::CharIterator` directly; instead, + // you create one implicitly through use of the `Cord::Chars()` member + // function. + // + // A `Cord::CharIterator` has the following properties: // - // Additional notes: - // * A `CharIterator` object is invalidated after any non-const - // operation on the `Cord` object over which it iterates. - // * Two `CharIterator` objects can be equality compared if and only if - // they remain valid and iterate over the same `Cord`. - // * The iterator keeps state that can grow for `Cord`s that contain many + // * The iterator is invalidated after any non-const operation on the + // Cord object over which it iterates. + // * Two `CharIterator` objects can be compared equal if and only if they + // remain valid and iterate over the same Cord. + // * The iterator keeps state that can grow for Cords that contain many // nodes and are imbalanced due to sharing. Prefer to pass this type by // const reference instead of by value. - // * This type cannot be a forward iterator because a `Cord` can reuse - // sections of memory. This violates the requirement that if dereferencing - // two iterators returns the same object, the iterators must compare - // equal. + // * This type cannot act as a forward iterator because a `Cord` can reuse + // sections of memory. This fact violates the requirement for forward + // iterators to compare equal if dereferencing them returns the same + // object. class CharIterator { public: using iterator_category = std::input_iterator_tag; @@ -378,34 +576,56 @@ class Cord { ChunkIterator chunk_iterator_; }; - // Advances `*it` by `n_bytes` and returns the bytes passed as a `Cord`. + // Cord::CharIterator::AdvanceAndRead() // - // `n_bytes` must be less than or equal to the number of bytes remaining for - // iteration. Otherwise the behavior is undefined. It is valid to pass - // `char_end()` and 0. + // Advances the `Cord::CharIterator` by `n_bytes` and returns the bytes + // advanced as a separate `Cord`. `n_bytes` must be less than or equal to the + // number of bytes within the Cord; otherwise, behavior is undefined. It is + // valid to pass `char_end()` and `0`. static Cord AdvanceAndRead(CharIterator* it, size_t n_bytes); - // Advances `*it` by `n_bytes`. + // Cord::CharIterator::Advance() // - // `n_bytes` must be less than or equal to the number of bytes remaining for - // iteration. Otherwise the behavior is undefined. It is valid to pass - // `char_end()` and 0. + // Advances the `Cord::CharIterator` by `n_bytes`. `n_bytes` must be less than + // or equal to the number of bytes remaining within the Cord; otherwise, + // behavior is undefined. It is valid to pass `char_end()` and `0`. static void Advance(CharIterator* it, size_t n_bytes); + // Cord::CharIterator::ChunkRemaining() + // // Returns the longest contiguous view starting at the iterator's position. // // `it` must be dereferenceable. static absl::string_view ChunkRemaining(const CharIterator& it); + // Cord::CharIterator::char_begin() + // // Returns an iterator to the first character of the `Cord`. + // + // Generally, prefer using `Cord::Chars()` within a range-based for loop for + // iterating over the chunks of a Cord. This method may be useful for getting + // a `CharIterator` where range-based for-loops may not be available. CharIterator char_begin() const; + + // Cord::CharIterator::char_end() + // // Returns an iterator to one past the last character of the `Cord`. + // + // Generally, prefer using `Cord::Chars()` within a range-based for loop for + // iterating over the chunks of a Cord. This method may be useful for getting + // a `CharIterator` where range-based for-loops are not useful. CharIterator char_end() const; - // Convenience wrapper over `Cord::char_begin()` and `Cord::char_end()` to - // enable range-based for-loop iterator over the characters of a `Cord`. + // Cord::CharIterator::CharRange // - // Prefer to use `Cord::Chars()` below instead of constructing this directly. + // `CharRange` is a helper class for iterating over the characters of a + // producing an iterator which can be used within a range-based for loop. + // Construction of a `CharRange` will return an iterator pointing to the first + // character of the Cord. Generally, do not construct a `CharRange` directly; + // instead, prefer to use the `Cord::Chars()` method show below. + // + // Implementation note: `CharRange` is simply a convenience wrapper over + // `Cord::char_begin()` and `Cord::char_end()`. class CharRange { public: explicit CharRange(const Cord* cord) : cord_(cord) {} @@ -417,8 +637,11 @@ class Cord { const Cord* cord_; }; - // Returns a range for iterating over the characters of a `Cord` with a - // range-based for-loop. + // Cord::CharIterator::Chars() + // + // Returns a `Cord::CharIterator` for iterating over the characters of a + // `Cord` with a range-based for-loop. For most character-based iteration + // tasks on a Cord, use `Cord::Chars()` to retrieve this iterator. // // Example: // @@ -435,23 +658,26 @@ class Cord { // } CharRange Chars() const; - // -------------------------------------------------------------------- - // Miscellaneous - - // Get the "i"th character of 'this' and return it. - // NOTE: This routine is reasonably efficient. It is roughly - // logarithmic in the number of nodes that make up the cord. Still, - // if you need to iterate over the contents of a cord, you should - // use a CharIterator/CordIterator rather than call operator[] or Get() - // repeatedly in a loop. + // Cord::operator[] + // + // Get the "i"th character of the Cord and returns it, provided that + // 0 <= i < Cord.size(). // - // REQUIRES: 0 <= i < size() + // NOTE: This routine is reasonably efficient. It is roughly + // logarithmic based on the number of chunks that make up the cord. Still, + // if you need to iterate over the contents of a cord, you should + // use a CharIterator/ChunkIterator rather than call operator[] or Get() + // repeatedly in a loop. char operator[](size_t i) const; + // Cord::TryFlat() + // // If this cord's representation is a single flat array, return a // string_view referencing that array. Otherwise return nullopt. absl::optional<absl::string_view> TryFlat() const; + // Cord::Flatten() + // // Flattens the cord into a single array and returns a view of the data. // // If the cord was already flat, the contents are not modified. @@ -574,6 +800,14 @@ class Cord { static bool GetFlatAux(absl::cord_internal::CordRep* rep, absl::string_view* fragment); + // Iterators for use inside Cord implementation + using InternalChunkIterator = + GenericChunkIterator<cord_internal::CordTreeMutablePath>; + using InternalChunkRange = GenericChunkRange<InternalChunkIterator>; + + InternalChunkIterator internal_chunk_begin() const; + InternalChunkRange InternalChunks() const; + // Helper for ForEachChunk() static void ForEachChunkAux( absl::cord_internal::CordRep* rep, @@ -608,6 +842,11 @@ class Cord { void AppendImpl(C&& src); }; +extern template class Cord::GenericChunkIterator< + cord_internal::CordTreeMutablePath>; +extern template class Cord::GenericChunkIterator< + cord_internal::CordTreeDynamicPath>; + ABSL_NAMESPACE_END } // namespace absl @@ -947,7 +1186,9 @@ inline bool Cord::StartsWith(absl::string_view rhs) const { return EqualsImpl(rhs, rhs_size); } -inline Cord::ChunkIterator::ChunkIterator(const Cord* cord) +template <typename StorageType> +inline Cord::GenericChunkIterator<StorageType>::GenericChunkIterator( + const Cord* cord) : bytes_remaining_(cord->size()) { if (cord->empty()) return; if (cord->contents_.is_tree()) { @@ -958,37 +1199,50 @@ inline Cord::ChunkIterator::ChunkIterator(const Cord* cord) } } -inline Cord::ChunkIterator Cord::ChunkIterator::operator++(int) { - ChunkIterator tmp(*this); +template <typename StorageType> +inline Cord::GenericChunkIterator<StorageType> +Cord::GenericChunkIterator<StorageType>::operator++(int) { + GenericChunkIterator tmp(*this); operator++(); return tmp; } -inline bool Cord::ChunkIterator::operator==(const ChunkIterator& other) const { +template <typename StorageType> +inline bool Cord::GenericChunkIterator<StorageType>::operator==( + const GenericChunkIterator<StorageType>& other) const { return bytes_remaining_ == other.bytes_remaining_; } -inline bool Cord::ChunkIterator::operator!=(const ChunkIterator& other) const { +template <typename StorageType> +inline bool Cord::GenericChunkIterator<StorageType>::operator!=( + const GenericChunkIterator<StorageType>& other) const { return !(*this == other); } -inline Cord::ChunkIterator::reference Cord::ChunkIterator::operator*() const { - assert(bytes_remaining_ != 0); +template <typename StorageType> +inline typename Cord::GenericChunkIterator<StorageType>::reference +Cord::GenericChunkIterator<StorageType>::operator*() const { + ABSL_HARDENING_ASSERT(bytes_remaining_ != 0); return current_chunk_; } -inline Cord::ChunkIterator::pointer Cord::ChunkIterator::operator->() const { - assert(bytes_remaining_ != 0); +template <typename StorageType> +inline typename Cord::GenericChunkIterator<StorageType>::pointer +Cord::GenericChunkIterator<StorageType>::operator->() const { + ABSL_HARDENING_ASSERT(bytes_remaining_ != 0); return ¤t_chunk_; } -inline void Cord::ChunkIterator::RemoveChunkPrefix(size_t n) { +template <typename StorageType> +inline void Cord::GenericChunkIterator<StorageType>::RemoveChunkPrefix( + size_t n) { assert(n < current_chunk_.size()); current_chunk_.remove_prefix(n); bytes_remaining_ -= n; } -inline void Cord::ChunkIterator::AdvanceBytes(size_t n) { +template <typename StorageType> +inline void Cord::GenericChunkIterator<StorageType>::AdvanceBytes(size_t n) { if (ABSL_PREDICT_TRUE(n < current_chunk_.size())) { RemoveChunkPrefix(n); } else if (n != 0) { @@ -1002,14 +1256,6 @@ inline Cord::ChunkIterator Cord::chunk_begin() const { inline Cord::ChunkIterator Cord::chunk_end() const { return ChunkIterator(); } -inline Cord::ChunkIterator Cord::ChunkRange::begin() const { - return cord_->chunk_begin(); -} - -inline Cord::ChunkIterator Cord::ChunkRange::end() const { - return cord_->chunk_end(); -} - inline Cord::ChunkRange Cord::Chunks() const { return ChunkRange(this); } inline Cord::CharIterator& Cord::CharIterator::operator++() { |