Type constraint

[Salih Dincer]

On Sunday, 8 October 2023 at 10:09:02 UTC, IchorDev wrote:
> On Wednesday, 4 October 2023 at 01:46:42 UTC, Joel wrote:
>> I think the if without static is still static, since it's part 
>> of the function name part, or so (outside of the curly bracket 
>> scope).
>
> You can't have regular if-statements inside templates. Regular 
> if-statements are checked at runtime but templates only exist 
> at compile-time.
>
> The way to write a *template constraint*—which is what you 
> want, and uses the `if` keyword—is thus:
>
> ```d
> struct List(T)
> if(__traits(isIntegral, T)){
>   auto addUp()
>     //(Add numbers)
>   }
> }
> ```
> Notice that the curly brace for the template comes after the 
> template constraint, and that there are only 2 curly braces 
> rather than the 3 from your example.

This snippet does not compile.  The curly brackets must be an 
even number, that is, they must terminate each other.

SDB at 79