static interface

[grauzone]

Andrei Alexandrescu wrote:
> grauzone wrote:
>> Andrei Alexandrescu wrote:
>>> grauzone wrote:
>>>> Leandro Lucarella wrote:
>>>>> Why not? ;)
>>>>
>>>> The actual question is if Andrei/Walter are interested at all in 
>>>> this. Because they didn't show any interest so far. D will probably 
>>>> be doomed to compile time bug-typing I mean duck-typing forever.
>>>
>>> There's an embarrassment of riches when it comes to finding stuff to 
>>> work on for D2. I think we need to resign ourselves to the idea that 
>>> we need to focus only on one subset of the stream of good ideas that 
>>> are being proposed.
>>
>> That's understandable of course.
>>
>>> FWIW I was keen on structs interacting in interesting ways with 
>>> interfaces (and submitted a number of enhancements in that 
>>> directions) but then realized there are a number of problems that 
>>> structs/interfaces cannot solve. I believe that a better path to 
>>> pursue in checking interface conformance is via reflection.
>>
>> That's a possible solution (and an easy way out to get rid of language 
>> design problems), but I'm sure it's not the best solution. (It also 
>> should be a little bit extended to give the user better error 
>> messages.) I hope cleaner solutions will be considered later, possibly 
>> after D2 is done.
>>
>> Which are the problems you mentioned?
> 
> I knew this was going to be asked. One issue I remember was that it's 
> difficult to talk about "a struct must define a type with certain 
> properties". You will say "but you can express that type as another 
> interface" but that solves the problem by increasing the size of the 
> feature. It gets even more complicated when you want to say "defines a 
> type with these or these other properties, depending on the properties 
> of this type parameter." I think that all can be solved through 
> something that is very similar to C++ concepts, and I would want to 
> avoid going that route.

In other words, a general solution inside the language would be too 
complex (because it had to support all sorts of type interfaces), so 
you'll just leave it to the user, who will implement the same thing with 
is() and friends?

> Andrei