Feature request: interfaces declare types

[Henning Hasemann]

On Thu, 24 May 2007 07:49:50 +1000
Reiner Pope <some at address.com> wrote:

> 
> My code doesn't entirely suit your use-case, but it does something similar:
> 
> class Foo (ContainerType)  {
>      ContainerType someNumbers;
> 
>      int popNumber() {
>          ContainerType.Iterator nr = someNumbers.firstIterator();
>          ...
>      }
> }
> 
> Your given usage example is a long way from D's type system: interfaces 
> are dynamic in nature, so you would expect the Iterator type specified 
> by it only to be known dynamically. But when you use types, you have to 
> know them statically.

The point with my example is working with a container you dont know the
explicit type of. Imagine some function returns a bunch of items like this:
Container(int) getMyItems();
Now you want to work with this bunch of items and you want to use iterators.
So your example doesnt seem to help me, because I need to know the Iterator type
in advance in order to use Container(). But if I knew that at that time
I knew the Container type as well, so I wouldnt have to work with the interface.

But I see the problem you mentioned:
If I have Container(int) a = getMyItems(); a.Iterator would be one type
and if I then do a = getSomeOtherItem(); a.Iterator might be another
which the type system shouldnt be able to handle because
that choice might depend on runtime cirumstances.


> I think what you are after would be better solved by some kind of Concepts.

Sorry I'm not sure I get what you mean with "some kind of Concepts", could
you be more specific?

Henning

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