John McCutchan | 9f60559 | 2015-09-17 14:09:47 -0700 | [diff] [blame] | 1 | This package exposes a `StringScanner` type that makes it easy to parse a string |
| 2 | using a series of `Pattern`s. For example: |
| 3 | |
| 4 | ```dart |
| 5 | import 'dart:math'; |
| 6 | |
| 7 | import 'package:string_scanner/string_scanner.dart'; |
| 8 | |
| 9 | num parseNumber(String source) { |
| 10 | // Scan a number ("1", "1.5", "-3"). |
| 11 | var scanner = new StringScanner(source); |
| 12 | |
| 13 | // [Scanner.scan] tries to consume a [Pattern] and returns whether or not it |
| 14 | // succeeded. It will move the scan pointer past the end of the pattern. |
| 15 | var negative = scanner.scan("-"); |
| 16 | |
| 17 | // [Scanner.expect] consumes a [Pattern] and throws a [FormatError] if it |
| 18 | // fails. Like [Scanner.scan], it will move the scan pointer forward. |
| 19 | scanner.expect(new RegExp(r"\d+")); |
| 20 | |
| 21 | // [Scanner.lastMatch] holds the [MatchData] for the most recent call to |
| 22 | // [Scanner.scan], [Scanner.expect], or [Scanner.matches]. |
| 23 | var number = int.parse(scanner.lastMatch[0]); |
| 24 | |
| 25 | if (scanner.scan(".")) { |
| 26 | scanner.expect(new RegExp(r"\d+")); |
| 27 | var decimal = scanner.lastMatch[0]; |
| 28 | number += int.parse(decimal) / math.pow(10, decimal.length); |
| 29 | } |
| 30 | |
| 31 | // [Scanner.expectDone] will throw a [FormatError] if there's any input that |
| 32 | // hasn't yet been consumed. |
| 33 | scanner.expectDone(); |
| 34 | |
| 35 | return (negative ? -1 : 1) * number; |
| 36 | } |
| 37 | ``` |