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Description:

string scanner

This package exposes a StringScanner type that makes it easy to parse a string
using a series of Patterns. For example:
import 'dart:math' as math;

import 'package:string_scanner/string_scanner.dart';

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.expect(RegExp(r'\d+'));

// [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('.')) {
scanner.expect(RegExp(r'\d+'));
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.
scanner.expectDone();

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