Async and Practical

Argument Parser Lite

Real CLI parsing uses a package, but a tiny --flag value reader is just a for-loop over an argument list. Each pair fills a Map<String, String>, then the program reads it with safe defaults.

Program

Play the program to parse a fixed argument list into a small options map.

argument_parser_lite.dart
Replay: real traced execution (multi-file project)
void main() {
  var args = ['--name', 'Ada', '--count', '3'];
  var options = <String, String>{};
  for (var i = 0; i + 1 < args.length; i += 2) {
    var key = args[i].substring(2);
    options[key] = args[i + 1];
  }
  var name = options['name'] ?? '';
  var count = int.parse(options['count'] ?? '0');
  print('$name x$count');
}

  1. args ← 4 tokens

    1void main() {2  var args = ['--name', 'Ada', '--count', '3'];3  var options = <String, String>{};
    values this step4 tokensargs

  2. options ← {}

    2var args = ['--name', 'Ada', '--count', '3'];3var options = <String, String>{};4for (var i = 0; i + 1 < args.length; i += 2) {
    values this step{}options

  3. loop ← parse pairs

    3var options = <String, String>{};4for (var i = 0; i + 1 < args.length; i += 2) {5  var key = args[i].substring(2);
    values this stepparse pairsloop

  4. options ← {name: Ada, count: 3}

    5  var key = args[i].substring(2);6  options[key] = args[i + 1];7}
    values this step{name: Ada, count: 3}options

  5. name ← Ada

    7}8var name = options['name'] ?? '';9var count = int.parse(options['count'] ?? '0');
    values this stepAdaname

  6. count ← 3

    8var name = options['name'] ?? '';9var count = int.parse(options['count'] ?? '0');10print('$name x$count');
    values this step3count

  7. print('$name x$count');

    9  var count = int.parse(options['count'] ?? '0');10  print('$name x$count');11}
    outputAda x3
    values this stepAdaname3count
flag pairs Each `--flag value` pair becomes one entry in the options map, keyed by the flag name.
substring(2) `args[i].substring(2)` drops the leading `--` from each flag before storing it.
safe defaults `options['count'] ?? '0'` falls back to a sensible string when the flag is missing.