optional_and_named.dart

import 'package:dynamic_function/dynamic_function.dart';
import 'dart:convert' as convert;

// equivalent to:
// void echo(dynamic x, [String? title], {bool asJson});
final dynamic echo = DynamicFunction((
  List<dynamic> positional,
  Map<Symbol, dynamic> named,
) {
  if (positional.length < 1 || positional.length > 2) {
    throw '${positional.length} arguments supplied to echo()';
  }
  dynamic x = positional[0];
  String? title = positional.length == 2 ? positional[1] as String : null;
  checkNamed(named, ['asJson']);
  bool asJson =
      named[Symbol('asJson')] == null ? false : named[Symbol('asJson')] as bool;
  String json = (x is String) ? '`${x}`' : '${x}';
  if (asJson) {
    json = convert.jsonEncode(x);
  }
  if (title == null) {
    print(json);
  } else {
    print('${title} ==> ${json}');
  }
  return null;
});

void main() {
  final x = [11, null, 'abc'];
  echo(x); // (1)
  echo(x, 'x'); // (2)
  echo(x, asJson: true); // (3)
  echo(x, 'x', asJson: true); // (4)
  //echo(); // 0 arguments supplied to echo()
  //echo(x, 'x', 777); // 3 arguments supplied to echo()
}

/*
[Result]
[11, null, abc] // (1)
x ==> [11, null, abc] // (2)
[11,null,"abc"] // (3)
x ==> [11,null,"abc"] // (4)
 */

pubspec.yaml

name: my_app
description: A sample command-line application
version: 0.0.1
publish_to: none

environment:
  sdk: ^3.7.2

dependencies:
  dynamic_function: ^2025.426.2037

dev_dependencies: