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195 lines
7.7 KiB
C++
195 lines
7.7 KiB
C++
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_I18N_BREAK_ITERATOR_H_
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#define BASE_I18N_BREAK_ITERATOR_H_
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#include <stddef.h>
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#include "base/i18n/base_i18n_export.h"
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#include "base/macros.h"
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#include "base/strings/string16.h"
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#include "base/strings/string_piece.h"
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// The BreakIterator class iterates through the words, word breaks, and
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// line breaks in a UTF-16 string.
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//
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// It provides several modes, BREAK_WORD, BREAK_LINE, BREAK_NEWLINE, and
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// BREAK_SENTENCE which modify how characters are aggregated into the returned
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// string.
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//
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// Under BREAK_WORD mode, once a word is encountered any non-word
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// characters are not included in the returned string (e.g. in the
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// UTF-16 equivalent of the string " foo bar! ", the word breaks are at
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// the periods in ". .foo. .bar.!. .").
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// Note that Chinese/Japanese/Thai do not use spaces between words so that
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// boundaries can fall in the middle of a continuous run of non-space /
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// non-punctuation characters.
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//
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// Under BREAK_LINE mode, once a line breaking opportunity is encountered,
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// any non-word characters are included in the returned string, breaking
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// only when a space-equivalent character or a line breaking opportunity
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// is encountered (e.g. in the UTF16-equivalent of the string " foo bar! ",
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// the breaks are at the periods in ". .foo .bar! .").
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//
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// Note that lines can be broken at any character/syllable/grapheme cluster
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// boundary in Chinese/Japanese/Korean and at word boundaries in Thai
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// (Thai does not use spaces between words). Therefore, this is NOT the same
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// as breaking only at space-equivalent characters where its former
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// name (BREAK_SPACE) implied.
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//
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// Under BREAK_NEWLINE mode, all characters are included in the returned
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// string, breaking only when a newline-equivalent character is encountered
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// (eg. in the UTF-16 equivalent of the string "foo\nbar!\n\n", the line
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// breaks are at the periods in ".foo\n.bar\n.\n.").
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//
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// Under BREAK_SENTENCE mode, all characters are included in the returned
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// string, breaking only on sentence boundaries defined in "Unicode Standard
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// Annex #29: Text Segmentation." Whitespace immediately following the sentence
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// is also included. For example, in the UTF-16 equivalent of the string
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// "foo bar! baz qux?" the breaks are at the periods in ".foo bar! .baz quz?."
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//
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// To extract the words from a string, move a BREAK_WORD BreakIterator
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// through the string and test whether IsWord() is true. E.g.,
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// BreakIterator iter(str, BreakIterator::BREAK_WORD);
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// if (!iter.Init())
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// return false;
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// while (iter.Advance()) {
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// if (iter.IsWord()) {
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// // Region [iter.prev(), iter.pos()) contains a word.
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// VLOG(1) << "word: " << iter.GetString();
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// }
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// }
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namespace base {
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namespace i18n {
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class BASE_I18N_EXPORT BreakIterator {
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public:
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enum BreakType {
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BREAK_WORD,
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BREAK_LINE,
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// TODO(jshin): Remove this after reviewing call sites.
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// If call sites really need break only on space-like characters
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// implement it separately.
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BREAK_SPACE = BREAK_LINE,
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BREAK_NEWLINE,
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BREAK_CHARACTER,
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// But don't remove this one!
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RULE_BASED,
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BREAK_SENTENCE,
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};
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enum WordBreakStatus {
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// The end of text that the iterator recognizes as word characters.
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// Non-word characters are things like punctuation and spaces.
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IS_WORD_BREAK,
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// Characters that the iterator can skip past, such as punctuation,
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// whitespace, and, if using RULE_BASED mode, characters from another
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// character set.
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IS_SKIPPABLE_WORD,
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// Only used if not in BREAK_WORD or RULE_BASED mode. This is returned for
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// newlines, line breaks, and character breaks.
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IS_LINE_OR_CHAR_BREAK
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};
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// Requires |str| to live as long as the BreakIterator does.
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BreakIterator(const StringPiece16& str, BreakType break_type);
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// Make a rule-based iterator. BreakType == RULE_BASED is implied.
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// TODO(andrewhayden): This signature could easily be misinterpreted as
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// "(const string16& str, const string16& locale)". We should do something
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// better.
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BreakIterator(const StringPiece16& str, const string16& rules);
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~BreakIterator();
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// Init() must be called before any of the iterators are valid.
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// Returns false if ICU failed to initialize.
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bool Init();
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// Advance to the next break. Returns false if we've run past the end of
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// the string. (Note that the very last "break" is after the final
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// character in the string, and when we advance to that position it's the
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// last time Advance() returns true.)
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bool Advance();
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// Updates the text used by the iterator, resetting the iterator as if
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// if Init() had been called again. Any old state is lost. Returns true
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// unless there is an error setting the text.
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bool SetText(const base::char16* text, const size_t length);
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// Under BREAK_WORD mode, returns true if the break we just hit is the
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// end of a word. (Otherwise, the break iterator just skipped over e.g.
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// whitespace or punctuation.) Under BREAK_LINE and BREAK_NEWLINE modes,
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// this distinction doesn't apply and it always returns false.
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bool IsWord() const;
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// Under BREAK_WORD mode:
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// - Returns IS_SKIPPABLE_WORD if non-word characters, such as punctuation or
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// spaces, are found.
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// - Returns IS_WORD_BREAK if the break we just hit is the end of a sequence
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// of word characters.
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// Under RULE_BASED mode:
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// - Returns IS_SKIPPABLE_WORD if characters outside the rules' character set
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// or non-word characters, such as punctuation or spaces, are found.
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// - Returns IS_WORD_BREAK if the break we just hit is the end of a sequence
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// of word characters that are in the rules' character set.
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// Not under BREAK_WORD or RULE_BASED mode:
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// - Returns IS_LINE_OR_CHAR_BREAK.
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BreakIterator::WordBreakStatus GetWordBreakStatus() const;
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// Under BREAK_WORD mode, returns true if |position| is at the end of word or
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// at the start of word. It always returns false under modes that are not
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// BREAK_WORD or RULE_BASED.
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bool IsEndOfWord(size_t position) const;
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bool IsStartOfWord(size_t position) const;
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// Under BREAK_SENTENCE mode, returns true if |position| is at a sentence
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// boundary. It always returns false under modes that are not BREAK_SENTENCE
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// or RULE_BASED.
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bool IsSentenceBoundary(size_t position) const;
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// Under BREAK_CHARACTER mode, returns whether |position| is a Unicode
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// grapheme boundary.
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bool IsGraphemeBoundary(size_t position) const;
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// Returns the string between prev() and pos().
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// Advance() must have been called successfully at least once for pos() to
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// have advanced to somewhere useful.
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string16 GetString() const;
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StringPiece16 GetStringPiece() const;
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// Returns the value of pos() returned before Advance() was last called.
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size_t prev() const { return prev_; }
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// Returns the current break position within the string,
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// or BreakIterator::npos when done.
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size_t pos() const { return pos_; }
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private:
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// ICU iterator, avoiding ICU ubrk.h dependence.
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// This is actually an ICU UBreakiterator* type, which turns out to be
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// a typedef for a void* in the ICU headers. Using void* directly prevents
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// callers from needing access to the ICU public headers directory.
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void* iter_;
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// The string we're iterating over. Can be changed with SetText(...)
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StringPiece16 string_;
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// Rules for our iterator. Mutually exclusive with break_type_.
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const string16 rules_;
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// The breaking style (word/space/newline). Mutually exclusive with rules_
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BreakType break_type_;
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// Previous and current iterator positions.
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size_t prev_, pos_;
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DISALLOW_COPY_AND_ASSIGN(BreakIterator);
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};
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} // namespace i18n
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} // namespace base
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#endif // BASE_I18N_BREAK_ITERATOR_H_
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