kwalrath

import 'dart:math';

abstract class Shape {
  factory Shape(String type) {
    if (type == 'circle') return Circle(2);
    if (type == 'square') return Square(2);
    throw 'Can\'t create $type.';
  }
  num get area;
}

kwalrath

import 'dart:math' show Random;

main() async {
  print('Compute π using the Monte Carlo method.');
  await for (final estimate in computePi().take(100)) {
    print('π ≅ $estimate');
  }
}

/// Generates a stream of increasingly accurate estimates of π.

kwalrath

class WannabeFunction {
  String call(String a, String b, String c) => '$a $b $c!';
}

var wf = WannabeFunction();
var out = wf('Hi', 'there,', 'gang');

main() => print(out);

kwalrath

// Add a contravariant variance modifier
class Writer<in T> {  
  void write(T x) => print(x);
}

main() {
  // Error! Cannot assign Writer<int> to Writer<Object> because the type
  // parameter is contravariantly declared.
  Writer<Object> objectWriter = new Writer<int>(); 
}

kwalrath

void main() {
  var iterable = ['Salad', 'Popcorn', 'Toast'];
  for (var element in iterable) {
    print(element);
  }
}

kwalrath

void main() {
  Iterable iterable = ['Salad', 'Popcorn', 'Toast'];
  print('The first element is ${iterable.first}');
  print('The last element is ${iterable.last}');
}

kwalrath

bool predicate(String element) {
  return element.length > 5;
}

main() {
  var items = ['Salad', 'Popcorn', 'Toast', 'Lasagne'];

  // You can find with a simple expression:
  var element1 = items.firstWhere((element) => element.length > 5);
  print(element1);

kwalrath

Use the methods `contains` and `startWith` from the `String` class.

kwalrath

void main() {
  var items = ['Salad', 'Popcorn', 'Toast'];
  
  if (items.any((element) => element.contains('a'))) {
    print('At least one element contains "a"');
  }
  
  if (items.every((element) => element.length >= 5)) {
    print('All elements have length >= 5');
  }

kwalrath

Use the methods `any` and `every` to compare the user age.