Implementing interfaces using alias this

[Steven Schveighoffer via Digitalmars-d-learn]

On 6/14/17 5:34 AM, Balagopal Komarath wrote:
> 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;
> }

An alias never causes implementation to be emitted. It should just be a 
forward from one symbol name to another. You need an actual function 
that can go into the vtable that takes a 'Test!Duck' as the context 
pointer. This wrapper has to be written by you.

-Steve