Re: Create constraint for each parameter in template arg pack

[vit via Digitalmars-d-learn]

On Tuesday, 28 August 2018 at 12:28:19 UTC, Andrey wrote:

Hello,
Let we have two variadic templates:

template Qwerty(Values...) {}
template Qaz(alias type, Data...) {}

Now I want to add a constraint to "Qwerty" so that each type in "Values" pack must be a "Qaz" template. I don't care about values of "type" or "Data" in "Qaz".

How to do it in D?

Generic solution:


template Qwerty(Values...)
if(allSatisfy!(isInstanceOf!Qaz, Values)){

}
class Qaz(alias type, Data...) {}



import std.meta : allSatisfy;
public import std.traits : isInstanceOf;
template isInstanceOf(alias T){
    import std.traits : impl = isInstanceOf;
    static enum isInstanceOf(alias X) = impl!(T, X);
    static enum isInstanceOf(X) = impl!(T, X);
}