class Inner {}

​

class Outer {

  Inner inner; alias inner this;

  this(Inner i) { inner = i; }

}

​

void main() {

  auto inner = new Inner;

  auto outer = new Outer(new Inner);

  Inner[] inners = [inner, outer];

​

  assert(inners[0], "first element is null");

  assert(inners[1], "second element is null");

}