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?

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));

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?

I'm not sure if there is a better way, but isInstanceOf (std.traits) seems to work with a static foreach and a static if.

template Qwerty(Values...)
{
    static foreach (value; Values)
    {
        static if (!isInstanceOf!(Qaz, value))
        {
            static assert(0, "Values are not Qaz only ...");
        }
    }

    // ...
}

On Tuesday, 28 August 2018 at 13:05:15 UTC, bauss wrote:
> 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?
>
> I'm not sure if there is a better way, but isInstanceOf (std.traits) seems to work with a static foreach and a static if.
>
> template Qwerty(Values...)
> {
>     static foreach (value; Values)
>     {
>         static if (!isInstanceOf!(Qaz, value))
>         {
>             static assert(0, "Values are not Qaz only ...");
>         }
>     }
>
>     // ...
> }

https://dlang.org/phobos/std_traits.html#TemplateOf

maybe...

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);
}

On Tuesday, 28 August 2018 at 13:05:15 UTC, bauss wrote:
> I'm not sure if there is a better way, but isInstanceOf (std.traits) seems to work with a static foreach and a static if.
>
> template Qwerty(Values...)
> {
>     static foreach (value; Values)
>     {
>         static if (!isInstanceOf!(Qaz, value))
>         {
>             static assert(0, "Values are not Qaz only ...");
>         }
>     }
>
>     // ...
> }

Thank you everybody!