sdk/lib/core/pattern.dart

// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

part of dart.core;

/// An interface for basic searches within strings.
abstract class Pattern {
  /// Matches this pattern against the string repeatedly.
  ///
  /// If [start] is provided, matching will start at that index.
  ///
  /// The returned iterable lazily finds non-overlapping matches
  /// of the pattern in the [string].
  /// If a user only requests the first match,
  /// this function should not compute all possible matches.
  ///
  /// The matches are found by repeatedly finding the first match
  /// of the pattern in the string, initially starting from [start],
  /// and then from the end of the previous match (but always
  /// at least one position later than the *start* of the previous
  /// match, in case the pattern matches an empty substring).
  Iterable<Match> allMatches(String string, [int start = 0]);

  /// Matches this pattern against the start of `string`.
  ///
  /// Returns a match if the pattern matches a substring of [string]
  /// starting at [start], and `null` if the pattern doesn't match
  /// a that point.
  ///
  /// The [start] must be non-negative and no greater than `string.length`.
  Match? matchAsPrefix(String string, [int start = 0]);
}

/// A result from searching within a string.
///
/// A `Match` or an [Iterable] of `Match` objects is returned from
/// the [Pattern] matching methods
/// ([Pattern.allMatches] and [Pattern.matchAsPrefix]).
///
/// The following example finds all matches of a [RegExp] in a [String]
/// and iterates through the returned iterable of `Match` objects.
/// ```dart
/// RegExp exp = RegExp(r"(\w+)");
/// String str = "Parse my string";
/// Iterable<Match> matches = exp.allMatches(str);
/// for (Match m in matches) {
///   String match = m[0]!;
///   print(match);
/// }
/// ```
/// The output of the example is:
/// ```
/// Parse
/// my
/// string
/// ```
/// Some patterns, regular expressions in particular, may record substrings
/// that were part of the matching. These are called _groups_ in the `Match`
/// object. Some patterns may never have any groups, and their matches always
/// have zero [groupCount].
abstract class Match {
  /// The index in the string where the match starts.
  int get start;

  /// The index in the string after the last character of the match.
  int get end;

  /// The string matched by the given [group].
  ///
  /// If [group] is 0, returns the entire match of the pattern.
  ///
  /// The result may be `null` if the pattern didn't assign a value to it
  /// as part of this match.
  String? group(int group);

  /// The string matched by the given [group].
  ///
  /// If [group] is 0, returns the match of the pattern.
  ///
  /// Short alias for [Match.group].
  String? operator [](int group);

  /// A list of the groups with the given indices.
  ///
  /// The list contains the strings returned by [group] for each index in
  /// [groupIndices].
  List<String?> groups(List<int> groupIndices);

  /// Returns the number of captured groups in the match.
  ///
  /// Some patterns may capture parts of the input that was used to
  /// compute the full match. This is the number of captured groups,
  /// which is also the maximal allowed argument to the [group] method.
  int get groupCount;

  /// The string on which this match was computed.
  String get input;

  /// The pattern used to search in [input].
  Pattern get pattern;
}