Add an additional optional argument to SpanScanner.spanFrom.

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//795343003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/string_scanner@42305 260f80e4-7a28-3924-810f-c04153c831b5
3 files changed
tree: a27f66f54a167cce5ad73f845757a0789c320f00
  1. CHANGELOG.md
  2. LICENSE
  3. README.md
  4. lib/
  5. pubspec.yaml
  6. test/
README.md

This package exposes a StringScanner type that makes it easy to parse a string using a series of Patterns. For example:

import 'dart:math';

import 'package:string_scanner/string_scanner.dart';

num parseNumber(String source) {
  // Scan a number ("1", "1.5", "-3").
  var scanner = new StringScanner(source);

  // [Scanner.scan] tries to consume a [Pattern] and returns whether or not it
  // succeeded. It will move the scan pointer past the end of the pattern.
  var negative = scanner.scan("-");

  // [Scanner.expect] consumes a [Pattern] and throws a [FormatError] if it
  // fails. Like [Scanner.scan], it will move the scan pointer forward.
  scanner.expect(new RegExp(r"\d+"));

  // [Scanner.lastMatch] holds the [MatchData] for the most recent call to
  // [Scanner.scan], [Scanner.expect], or [Scanner.matches].
  var number = int.parse(scanner.lastMatch[0]);

  if (scanner.scan(".")) {
    scanner.expect(new RegExp(r"\d+"));
    var decimal = scanner.lastMatch[0];
    number += int.parse(decimal) / math.pow(10, decimal.length);
  }

  // [Scanner.expectDone] will throw a [FormatError] if there's any input that
  // hasn't yet been consumed.
  scanner.expectDone();

  return (negative ? -1 : 1) * number;
}