Shameless autopromotion : type safe tagged union in D

[deadalnix]

On Friday, 10 May 2013 at 13:11:37 UTC, Dmitry Olshansky wrote:
> E.g. this is exactly the same switch madness we sought to avoid:
>

The article don't plan to avoid this, but to make the tagged 
union safe. I agree this is a plus, but didn't really took time 
to make that work.

> void process(T)(T data) {
>     alias Type = typeof(data);
>
>     static if(is(Type == A)) {
>         // Code that handle the case where it is an A.
>     } else static if(is(Type == B)) {
>         // Code that handle the case where it is an B.
>     } else {
>         static assert(0, "You must handle type " ~ 
> Type.stringof);
>     }
> }
>
> t.apply!process();
>
>
> I'd rather see another idiom supported too:
>
> t.apply!(processA, processB)();
>
> where e.g.
> void proccessA(A value){ ... }
>
> void processB(B value){ ... }
>

That can work indeed.

> Anther thing is that will allow succinct notations like:
>
> int squared = t.apply!(
> 	(A a) => a.x*a.x + a.y*a.y,
> 	(B b) => b.x*b.x + b.y*b.y + b.z*b.z
> )();
>
> I sure don't fancy putting static if into lambdas.
> Another thing about it is it allows specifying safe catch all 
> or default case.

That last one won't work. DMD don't accept locals here, even if 
they are functions.