sdk/lib/_internal/compiler/implementation/scanner/string_scanner.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 scanner;

/**
 * Scanner that reads from a String and creates tokens that points to
 * substrings.
 */
class StringScanner extends ArrayBasedScanner<SourceString> {
  final String string;

  StringScanner(String this.string, {bool includeComments: false})
    : super(includeComments);

  int nextByte() => charAt(++byteOffset);

  int peek() => charAt(byteOffset + 1);

  int charAt(index)
      => (string.length > index) ? string.charCodeAt(index) : $EOF;

  SourceString asciiString(int start, int offset) {
    return new SubstringWrapper(string, start, byteOffset + offset);
  }

  SourceString utf8String(int start, int offset) {
    return new SubstringWrapper(string, start, byteOffset + offset + 1);
  }

  void appendByteStringToken(PrecedenceInfo info, SourceString value) {
    // assert(kind != $a || keywords.get(value) == null);
    tail.next = new StringToken.fromSource(info, value, tokenStart);
    tail = tail.next;
  }
}

class SubstringWrapper implements SourceString {
  final String internalString;
  final int begin;
  final int end;
  int cashedHash = 0;
  String cachedSubString;

  SubstringWrapper(String this.internalString,
                   int this.begin, int this.end);

  int get hashCode {
    if (0 == cashedHash) {
      cashedHash = slowToString().hashCode;
    }
    return cashedHash;
  }

  bool operator ==(other) {
    return other is SourceString && slowToString() == other.slowToString();
  }

  void printOn(StringBuffer sb) {
    sb.add(internalString.substring(begin, end));
  }

  String slowToString() {
    if (cachedSubString == null) {
      cachedSubString = internalString.substring(begin, end);
    }
    return cachedSubString;
  }

  String toString() => "SubstringWrapper(${slowToString()})";

  String get stringValue => null;

  Iterator<int> iterator() =>
      new StringCodeIterator.substring(internalString, begin, end);

  SourceString copyWithoutQuotes(int initial, int terminal) {
    assert(0 <= initial);
    assert(0 <= terminal);
    assert(initial + terminal <= internalString.length);
    return new SubstringWrapper(internalString,
                                begin + initial, end - terminal);
  }

  bool get isEmpty => begin == end;

  bool isPrivate() => !isEmpty && identical(internalString.charCodeAt(begin), $_);
}