_delegating_mixin.md

Proof of concept for using mixin to decorate with delegation rather than inheritance (the pattern I normally see)

main.dart

void main() {
  print( new Foo().foo);
  print( new ConcreteDelegating().foo);
  print( new ConcreteDelegating().bar);
}

class Foo {
  String get foo => 'original foo';
  String get bar => 'original bar';
}

abstract class DelegatingFoo implements Foo {
  Foo get delegate;
  String get foo => delegate.foo;
  String get bar => delegate.bar;
}

class ConcreteDelegating extends Object with DelegatingFoo {
  final Foo delegate = new Foo();
  String get foo => 'Decorated!' + delegate.foo;
}