I need to conditionally inherit:

interface A(T) : conditionallyInherit!(isBasicType!T, B);

A!(double) will inherit B but A!(mytype) won't.

and while I'm at it I need to conditionally constrain types.

interface A(T) where(!isBasicType!T, (T : B));

which is suppose to require T to inherit from B if T is not basic type.

This should work:

template conditionallyInherit(bool inherit, T) {
    static if (inherit)
        alias T conditionallyInherit;
    else
        interface conditionallyInherit {}
}

On Sunday, 14 July 2013 at 05:04:37 UTC, JS wrote:
> and while I'm at it I need to conditionally constrain types.
>
> interface A(T) where(!isBasicType!T, (T : B));
>
> which is suppose to require T to inherit from B if T is not basic type.

interface A(T) if (isBasicType!T || is(T : B))

On Sunday, 14 July 2013 at 05:28:08 UTC, lomereiter wrote:
> This should work:
>
> template conditionallyInherit(bool inherit, T) {
>     static if (inherit)
>         alias T conditionallyInherit;
>     else
>         interface conditionallyInherit {}
> }

Thanks, I tried something similar but it didn't work right...

I assume that you template ends up creating a dummy interface though and this isn't really acceptable.

e.g., interface A : conditionallyInherit!(false, B) { }

will cause A to inherit from conditionallyInherit?

On Sunday, 14 July 2013 at 05:30:57 UTC, lomereiter wrote:
> On Sunday, 14 July 2013 at 05:04:37 UTC, JS wrote:
>> and while I'm at it I need to conditionally constrain types.
>>
>> interface A(T) where(!isBasicType!T, (T : B));
>>
>> which is suppose to require T to inherit from B if T is not basic type.
>
> interface A(T) if (isBasicType!T || is(T : B))

Thanks, works. I remember seeing code like this somewhere but couldn't find any docs about it.

> I assume that you template ends up creating a dummy interface though and this isn't really acceptable.

Yes, it does. Once ':' is typed, some inheritance must occur.

Why isn't a dummy interface acceptable?

On 2013-07-14, 07:00, JS wrote:

> I need to conditionally inherit:
>
> interface A(T) : conditionallyInherit!(isBasicType!T, B);
>
> A!(double) will inherit B but A!(mytype) won't.

template conditionallyInherit(bool choice, T...) {
    static if (choice) {
        alias conditionallyInherit = T;
    } else {
        import std.typetuple : TypeTuple;
        alias conditionallyInherit = TypeTuple!();
    }
}

Should work.

-- 
Simen

On 2013-07-14, 07:40, JS wrote:

> On Sunday, 14 July 2013 at 05:30:57 UTC, lomereiter wrote:
>> On Sunday, 14 July 2013 at 05:04:37 UTC, JS wrote:
>>> and while I'm at it I need to conditionally constrain types.
>>>
>>> interface A(T) where(!isBasicType!T, (T : B));
>>>
>>> which is suppose to require T to inherit from B if T is not basic type.
>>
>> interface A(T) if (isBasicType!T || is(T : B))
>
> Thanks, works. I remember seeing code like this somewhere but couldn't find any docs about it.

Here. I admit there should probably be more examples, and perhaps also
some info on the classes/interfaces/structs & unions pages.

http://dlang.org/template.html#Constraint

-- 
Simen

On Sunday, 14 July 2013 at 09:52:29 UTC, Simen Kjaeraas wrote:
> On 2013-07-14, 07:40, JS wrote:
>
>> On Sunday, 14 July 2013 at 05:30:57 UTC, lomereiter wrote:
>>> On Sunday, 14 July 2013 at 05:04:37 UTC, JS wrote:
>>>> and while I'm at it I need to conditionally constrain types.
>>>>
>>>> interface A(T) where(!isBasicType!T, (T : B));
>>>>
>>>> which is suppose to require T to inherit from B if T is not basic type.
>>>
>>> interface A(T) if (isBasicType!T || is(T : B))
>>
>> Thanks, works. I remember seeing code like this somewhere but couldn't find any docs about it.
>
> Here. I admit there should probably be more examples, and perhaps also
> some info on the classes/interfaces/structs & unions pages.
>
> http://dlang.org/template.html#Constraint

thanks.