Idea: Lazy upcasting

[Reiner Pope]

Marcin Kuszczak wrote:
> Hello!
> 
> Recently I have tried to achieve chaining a few calls to setters. I mean
> something like below:
> 
> //-------------------------------------------
> 
> abstract class Storage {
>      Storage param1(int p1) {
>          this.p1 = p1;
>          return this;
>      }
> private:
>      int p1;
> }
> 
> class SpecificStorage : Storage {
> public:
>      SpecificStorage param2(bool p2) {
>         this.p2=p2;
>         return this;
>      }
> private:
>      bool p2;
> }
> 
> void main() {
> //                             ...ok...      ...ok...        ...ups!
> SpecificStorage1 s1 = (new SpecificStorage).param2(true).param1(5);
> }
> 
> //-------------------------------------------

How about:

interface Storage
{
     Storage param1(int);
}

abstract class StorageImpl(T) : Storage {
     static assert(is(typeof(this) == T));

     T param1(int p1)
     {
         this.p1 = p1;
         return cast(T)this;
     }
     private int p1;
}

class SpecificStorage : StorageImpl!(SpecificStorage) {
     SpecificStorage param2(bool p2) {
         this.p2 = p2;
         return this;
     }
     private bool p2;
}

That should already work.

Cheers,

Reiner