Implicit Interface Deduction

[Faux Amis via Digitalmars-d-learn]

On Mon 14/12/2015 02:45, Chris Wright wrote:
> On Sun, 13 Dec 2015 23:09:47 +0100, Faux Amis wrote:
>
>> interface IA {}
>> interface IB {}
>> interface IC {}
>> interface IAB : IA, IB {} interface IBC : IB, IC {}
>>
>> class C : IA, IB, IC {}
>> // Defining C as : IAB, IBC // is not really scalable ;)
>>
>> void main()
>> {
>>    IAB c = new C(); // This doesn't work.
>> }
>> // Any suggestions?
>
> If you really can't modify the declaration to suit, there are two options.
>
> The first is to use casts. If a function would require something that's
> both IA and IB, it takes an IA and casts to IB. It can use contracts to
> ensure that things are of the right type. Ugly, but it works.
>
> The second is to use templates to generate the interface you need and
> appropriate wrapper classes. Then you need to manually wrap variables in
> those generated wrapper classes wherever you need to pass them. You'll
> end up with an API like:
>
> alias IABC = Union!(IA, IB, IC);
> void foo(IABC.Interface iabc) {}
> auto c = new C;
> foo(IABC.wrap(c));
>
> If you really want to go this way, std.typecons might help. Or I hacked
> up something horrific here: http://dpaste.dzfl.pl/0464f723580f
>
The thing is, I would like to define my class by its basic components.
It makes it very clear what type of functionality it exposes.
I do not see how the Union template is different from
interface IABC : IA, IB, IC
Maybe I don't get :(