sample.dart

abstract class Foo {
  Function execute;
}

class Bar1 implements Foo { 
  Function execute = (String s) => print('Bar1 execute s: $s');
}

class Bar2 implements Foo {
  Function execute = (int i) => print('Bar2 execute i: $i, i*2: ${i*2}');
}



void main() {
  var bar1 = new Bar1();
  bar1.execute('Hello');
  bar1.execute(200);
  var bar2 = new Bar2();
  bar2.execute(4);
  bar2.execute('Hello');
}