Implementing interfaces using alias this

[Balagopal Komarath via Digitalmars-d-learn]

Why doesn't this work? The Test!Duck type has a void quack() 
method but the compiler says it is not implemented.

import std.stdio;

interface IDuck
{
     void quack();
}

class Test(T) : IDuck
{
     T data;
     alias data this;
}

struct Duck
{
     void quack()
     {
         writeln("Quack");
     }
}


void main()
{
	Test!Duck d;
}