D modeling

[CheeseWiz]

On Tuesday, 2 July 2019 at 13:52:17 UTC, FeepingCreature wrote:
> On Tuesday, 2 July 2019 at 01:21:56 UTC, CheeseWiz wrote:
>> 3. Oop contravariance breaks the model logic and mixes 
>> dependencies. It is a non-issue in modeling. In D it requires 
>> us to cast everywhere. This is the main issue. You can see the 
>> issue at work using IsItTasty functions. It's simple, 
>> Contravariance prevents us staying with the derived model, we 
>> have to use the base model(for return types, same applies to 
>> arguments with covariance). But when we are in a derived model 
>> we are in it, we are using everything in the derived model 
>> that belongs to it(and behind them is the base model, but we 
>> do not directly refer to the base model), at least that would 
>> be the plan.
>>
>
> Quite the opposite! Covariance actually saves you.
>
> struct ModelB
> {	
>     interface iAnimal : ModelA.iAnimal
>     {
>         override iFood LikesWhichFood();
>     }

Ok, adding the follow does seem to work:

     interface iAnimal : ModelA.iAnimal
     {
		override iFood LikesWhichFood();
     }

then one has to do

     class Animal : ModelA.Animal, iAnimal
     {
// Note the cast, but it is ok if necessary since at least it 
would isolate it.
		 override iFood LikesWhichFood() { return 
cast(iFood)super.LikesWhichFood; }
     }


The goal here is to avoid having to add all the extra plumbing. 
Imagine a real project with 100's of classes and having to 
override and cast everything just to get it to function. It seems 
excessive. Maybe meta programming can fix it?