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?

import std.meta : allSatisfy;

template Qwerty(Values...)
if(allSatisfy!(isQaz, Values)){

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

enum isQaz(alias Q : Qaz!Args, Args...) = true;
enum isQaz(Args...) = false;

alias Foo = Qwerty!(Qaz!(i => i), Qaz!(i => i), Qaz!(i => i));