blob: ec9dd7660e1a5bc23c1e3262365900f726546d81 [file] [log] [blame]
// Copyright (c) 2019, 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.
import 'dart:math' as math;
import 'package:string_scanner/string_scanner.dart';
void main(List<String> args) {
num parseNumber(String source) {
// Scan a number ("1", "1.5", "-3").
final scanner = 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.
final 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.lastMatch] holds the [MatchData] for the most recent call to
// [Scanner.scan], [Scanner.expect], or [Scanner.matches].
var number = num.parse(scanner.lastMatch![0]!);
if (scanner.scan('.')) {
final 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.
return (negative ? -1 : 1) * number;