Strange Dart 7

main.dart

// Almost by definition, if I'm able to pass X where Y is expected, then X is a
// subtype of Y.
//
// In Dart, this mostly holds, but `dynamic` is an exception. I can pass
// `dynamic` everywhere, but it's not really a subtype of anything.

void f(int a) {}

class C<A> {}

void g<A>(C<A> a) {}

void main() {
  dynamic x = 123;
  f(x); // type checks

  C<dynamic> y = C();
  g<int>(y); // type error: C<dynamic> can't be assigned to C<int>
}