#80: Attempt at abstracting over String, to be able to use Characters.

petitparser/lib/buffer.dart

@@ -0,0 +1,38 @@
+/// This package contains the parse input buffers.
+import 'package:characters/characters.dart';
+
+import 'src/buffer/character_buffer.dart';
+import 'src/buffer/string_buffer.dart';
+
+abstract class Buffer {
+  /// Create a buffer from the most appropriate internal implementation.
+  factory Buffer(/*Buffer|String|Characters*/ dynamic input) {
+    if (input is Buffer) {
+      return input;
+    } else if (input is String) {
+      return Buffer.fromString(input);
+    } else if (input is Characters) {
+      return Buffer.fromCharacters(input);
+    } else {
+      throw ArgumentError.value(input, 'input', 'Invalid input buffer');
+    }
+  }
+
+  /// Create a buffer from an input [String] (UTF-16).
+  factory Buffer.fromString(String input) => StringBuffer(input);
+
+  /// Create a buffer from input [Characters] (Unicode Grapheme).
+  factory Buffer.fromCharacters(Characters input) => CharactersBuffer(input);
+
+  /// Return the length of the buffer.
+  int get length;
+
+  /// Return the character at [position].
+  String charAt(int position);
+
+  /// Return the character code at [position].
+  int codeUnitAt(int position);
+
+  /// Return the substring between [start] and [stop] (exclusive).
+  String substring(int start, int stop);
+}

petitparser/lib/petitparser.dart

@@ -1,5 +1,6 @@
 /// This package exports the core library of PetitParser, a dynamic parser
 /// combinator framework.
+export 'buffer.dart';
 export 'context.dart';
 export 'core.dart';
 export 'definition.dart';

petitparser/lib/src/buffer/character_buffer.dart

@@ -0,0 +1,35 @@
+import 'package:characters/characters.dart';
+
+import '../../buffer.dart';
+
+class CharactersBuffer implements Buffer {
+  final List<String> characters;
+
+  CharactersBuffer(Characters characters)
+      : characters = characters.toList(growable: false);
+
+  @override
+  int get length => characters.length;
+
+  @override
+  String charAt(int position) => characters[position];
+
+  @override
+  int codeUnitAt(int position) {
+    final chars = characters[position];
+    final charsLength = chars.length;
+    if (charsLength == 1) {
+      return chars.codeUnitAt(0);
+    } else {
+      var value = 0;
+      for (var i = 0; i < charsLength; i++) {
+        value = (value << 16) | chars.codeUnitAt(i);
+      }
+      return value;
+    }
+  }
+
+  @override
+  String substring(int start, int end) =>
+      characters.getRange(start, end).join();
+}

petitparser/lib/src/buffer/string_buffer.dart

@@ -0,0 +1,22 @@
+import 'package:meta/meta.dart';
+
+import '../../buffer.dart';
+
+@immutable
+class StringBuffer implements Buffer {
+  final String string;
+
+  const StringBuffer(this.string);
+
+  @override
+  int get length => string.length;
+
+  @override
+  String charAt(int position) => string[position];
+
+  @override
+  int codeUnitAt(int position) => string.codeUnitAt(position);
+
+  @override
+  String substring(int start, int end) => string.substring(start, end);
+}

petitparser/lib/src/context/context.dart

@@ -1,5 +1,6 @@
 import 'package:meta/meta.dart';
 
+import '../../buffer.dart';
 import '../core/token.dart';
 import 'failure.dart';
 import 'result.dart';
@@ -11,7 +12,7 @@ class Context {
   const Context(this.buffer, this.position);
 
   /// The buffer we are working on.
-  final String buffer;
+  final Buffer buffer;
 
   /// The current position in the [buffer].
   final int position;

petitparser/lib/src/context/failure.dart

@@ -1,9 +1,10 @@
+import '../../buffer.dart';
 import '../core/exception.dart';
 import 'result.dart';
 
 /// An immutable parse result in case of a failed parse.
 class Failure<R> extends Result<R> {
-  const Failure(String buffer, int position, this.message)
+  const Failure(Buffer buffer, int position, this.message)
       : super(buffer, position);
 
   @override

petitparser/lib/src/context/result.dart

@@ -1,9 +1,10 @@
+import '../../buffer.dart';
 import '../core/exception.dart';
 import 'context.dart';
 
 /// An immutable parse result.
 abstract class Result<R> extends Context {
-  const Result(String buffer, int position) : super(buffer, position);
+  const Result(Buffer buffer, int position) : super(buffer, position);
 
   /// Returns `true` if this result indicates a parse success.
   bool get isSuccess => false;

petitparser/lib/src/context/success.dart

@@ -1,8 +1,9 @@
+import '../../buffer.dart';
 import 'result.dart';
 
 /// An immutable parse result in case of a successful parse.
 class Success<R> extends Result<R> {
-  const Success(String buffer, int position, this.value)
+  const Success(Buffer buffer, int position, this.value)
       : super(buffer, position);
 
   @override

petitparser/lib/src/core/exception.dart

@@ -1,3 +1,4 @@
+import '../../buffer.dart';
 import '../context/failure.dart';
 
 /// An exception raised in case of a parse error.
@@ -13,7 +14,7 @@ class ParserException implements FormatException {
   int get offset => failure.position;
 
   @override
-  String get source => failure.buffer;
+  Buffer get source => failure.buffer;
 
   @override
   String toString() => '${failure.message} at ${failure.toPositionString()}';

petitparser/lib/src/core/parser.dart

@@ -1,5 +1,6 @@
 import 'package:meta/meta.dart';
 
+import '../../buffer.dart';
 import '../context/context.dart';
 import '../context/failure.dart';
 import '../context/result.dart';
@@ -30,7 +31,7 @@ abstract class Parser<T> {
   ///
   /// Subclasses don't necessarily have to override this method, since it is
   /// emulated using its slower brother.
-  int fastParseOn(String buffer, int position) {
+  int fastParseOn(Buffer buffer, int position) {
     final result = parseOn(Context(buffer, position));
     return result.isSuccess ? result.position : -1;
   }
@@ -47,7 +48,9 @@ abstract class Parser<T> {
   /// Similarly, `letter().plus().parse('123')` results in an instance of
   /// [Failure], where [Context.position] is `0` and [Failure.message] is
   /// ['letter expected'].
-  Result<T> parse(String input) => parseOn(Context(input, 0));
+  @nonVirtual
+  Result<T> parse(/*Buffer|String|Characters*/ dynamic input) =>
+      parseOn(Context(Buffer(input), 0));
 
   /// Returns a shallow copy of the receiver.
   ///

petitparser/lib/src/core/token.dart

@@ -1,5 +1,6 @@
 import 'package:meta/meta.dart';
 
+import '../../buffer.dart';
 import '../matcher/matches_skipping.dart';
 import '../parser/action/token.dart';
 import '../parser/character/char.dart';
@@ -23,7 +24,7 @@ class Token<T> {
   final T value;
 
   /// The parsed buffer of the token.
-  final String buffer;
+  final Buffer buffer;
 
   /// The start position of the token in the buffer.
   final int start;
@@ -64,7 +65,7 @@ class Token<T> {
       char('\n') | (char('\r') & char('\n').optional());
 
   /// Converts the [position] index in a [buffer] to a line and column tuple.
-  static List<int> lineAndColumnOf(String buffer, int position) {
+  static List<int> lineAndColumnOf(Buffer buffer, int position) {
     var line = 1, offset = 0;
     for (final token in newlineParser().token().matchesSkipping(buffer)) {
       if (position < token.stop) {
@@ -78,7 +79,7 @@ class Token<T> {
 
   /// Returns a human readable string representing the [position] index in a
   /// [buffer].
-  static String positionString(String buffer, int position) {
+  static String positionString(Buffer buffer, int position) {
     final lineAndColumn = lineAndColumnOf(buffer, position);
     return '${lineAndColumn[0]}:${lineAndColumn[1]}';
   }

petitparser/lib/src/definition/parser.dart

@@ -1,3 +1,4 @@
+import '../../buffer.dart';
 import '../context/context.dart';
 import '../context/result.dart';
 import '../core/parser.dart';
@@ -14,7 +15,7 @@ class GrammarParser extends DelegateParser {
   Result parseOn(Context context) => delegate.parseOn(context);
 
   @override
-  int fastParseOn(String buffer, int position) =>
+  int fastParseOn(Buffer buffer, int position) =>
       delegate.fastParseOn(buffer, position);
 
   @override

petitparser/lib/src/definition/reference.dart

@@ -1,5 +1,6 @@
 import 'package:meta/meta.dart';
 
+import '../../buffer.dart';
 import '../context/context.dart';
 import '../context/result.dart';
 import '../core/parser.dart';
@@ -44,7 +45,7 @@ class Reference extends Parser {
       throw UnsupportedError('References cannot be parsed.');
 
   @override
-  int fastParseOn(String buffer, int position) =>
+  int fastParseOn(Buffer buffer, int position) =>
       throw UnsupportedError('References cannot be parsed.');
 
   @override

petitparser/lib/src/matcher/accept.dart

@@ -1,9 +1,11 @@
+import '../../buffer.dart';
 import '../core/parser.dart';
 
 extension AcceptParser<T> on Parser<T> {
   /// Tests if the [input] can be successfully parsed.
   ///
   /// For example, `letter().plus().accept('abc')` returns `true`, and
   /// `letter().plus().accept('123')` returns `false`.
-  bool accept(String input) => fastParseOn(input, 0) >= 0;
+  bool accept(/*Buffer|String|Characters*/ dynamic input) =>
+      fastParseOn(Buffer(input), 0) >= 0;
 }

petitparser/lib/src/matcher/matches.dart

@@ -1,3 +1,4 @@
+import '../../buffer.dart';
 import '../core/parser.dart';
 import '../parser/action/map.dart';
 import '../parser/combinator/and.dart';
@@ -13,14 +14,14 @@ extension MatchesParser<T> on Parser<T> {
   /// For example, `letter().plus().matches('abc de')` results in the list
   /// `[['a', 'b', 'c'], ['b', 'c'], ['c'], ['d', 'e'], ['e']]`. See
   /// [matchesSkipping] to retrieve non-overlapping parse results.
-  List<T> matches(String input) {
+  List<T> matches(/*Buffer|String|Characters*/ dynamic input) {
     final list = <T>[];
     and()
         .map(list.add, hasSideEffects: true)
         .seq(any())
         .or(any())
         .star()
-        .fastParseOn(input, 0);
+        .fastParseOn(Buffer(input), 0);
     return list;
   }
 }

petitparser/lib/src/matcher/matches_skipping.dart

@@ -1,3 +1,4 @@
+import '../../buffer.dart';
 import '../core/parser.dart';
 import '../parser/action/map.dart';
 import '../parser/combinator/choice.dart';
@@ -11,9 +12,12 @@ extension MatchesSkippingParser<T> on Parser<T> {
   /// For example, `letter().plus().matchesSkipping('abc de')` results in the
   /// list `[['a', 'b', 'c'], ['d', 'e']]`. See [matches] to retrieve
   /// overlapping parse results.
-  List<T> matchesSkipping(String input) {
+  List<T> matchesSkipping(/*Buffer|String|Characters*/ dynamic input) {
     final list = <T>[];
-    map(list.add, hasSideEffects: true).or(any()).star().fastParseOn(input, 0);
+    map(list.add, hasSideEffects: true)
+        .or(any())
+        .star()
+        .fastParseOn(Buffer(input), 0);
     return list;
   }
 }

petitparser/lib/src/matcher/pattern/parser_pattern.dart

@@ -1,5 +1,6 @@
 import 'package:meta/meta.dart';
 
+import '../../../buffer.dart';
 import '../../core/parser.dart';
 import 'parser_match.dart';
 import 'pattern_iterable.dart';
@@ -31,7 +32,7 @@ class ParserPattern implements Pattern {
   /// Returns `null` if the pattern doesn't match.
   @override
   ParserMatch? matchAsPrefix(String string, [int start = 0]) {
-    final end = parser.fastParseOn(string, start);
+    final end = parser.fastParseOn(Buffer.fromString(string), start);
     return end < 0 ? null : ParserMatch(this, string, start, end);
   }
 }

petitparser/lib/src/matcher/pattern/pattern_iterator.dart

@@ -1,3 +1,4 @@
+import '../../../buffer.dart';
 import '../../core/parser.dart';
 import 'parser_match.dart';
 import 'parser_pattern.dart';
@@ -6,17 +7,19 @@ class PatternIterator extends Iterator<ParserMatch> {
   final ParserPattern pattern;
   final Parser parser;
   final String input;
+  final Buffer buffer;
   int start;
 
-  PatternIterator(this.pattern, this.parser, this.input, this.start);
+  PatternIterator(this.pattern, this.parser, this.input, this.start)
+      : buffer = Buffer.fromString(input);
 
   @override
   late ParserMatch current;
 
   @override
   bool moveNext() {
-    while (start <= input.length) {
-      final end = parser.fastParseOn(input, start);
+    while (start <= buffer.length) {
+      final end = parser.fastParseOn(buffer, start);
       if (end < 0) {
         start++;
       } else {

petitparser/lib/src/parser/action/cast.dart

@@ -1,3 +1,4 @@
+import '../../../buffer.dart';
 import '../../context/context.dart';
 import '../../context/result.dart';
 import '../../core/parser.dart';
@@ -23,7 +24,7 @@ class CastParser<R> extends DelegateParser<R> {
   }
 
   @override
-  int fastParseOn(String buffer, int position) =>
+  int fastParseOn(Buffer buffer, int position) =>
       delegate.fastParseOn(buffer, position);
 
   @override

petitparser/lib/src/parser/action/cast_list.dart

@@ -1,3 +1,4 @@
+import '../../../buffer.dart';
 import '../../context/context.dart';
 import '../../context/result.dart';
 import '../../core/parser.dart';
@@ -24,7 +25,7 @@ class CastListParser<R> extends DelegateParser<List<R>> {
   }
 
   @override
-  int fastParseOn(String buffer, int position) =>
+  int fastParseOn(Buffer buffer, int position) =>
       delegate.fastParseOn(buffer, position);
 
   @override