Language Tour: Restricting the parameterized type

main.dart

// From https://www.dartlang.org/guides/language/language-tour#restricting-the-parameterized-type

class SomeBaseClass {}

// T must be SomeBaseClass or one of its descendants.
class Foo<T extends SomeBaseClass> {
  String toString() => 'Foo<$T>';
}

class Extender extends SomeBaseClass {}

void main() {
  // It's OK to use SomeBaseClass or any of its subclasses inside <>.
  var someBaseClassFoo = new Foo<SomeBaseClass>();
  var extenderFoo = new Foo<Extender>();

  // It's also OK to use no <> at all.
  var foo = new Foo();
  print('$someBaseClassFoo, $extenderFoo, $foo');
  // Expecting: Foo<SomeBaseClass>, Foo<Extender>, Foo<dynamic>
  // Actual: Foo<SomeBaseClass>, Foo<Extender>, Foo<SomeBaseClass>
}