How to instantiate a template struct with a template constructor without relying on auto deduction?

[Simen Kjærås]

On Wednesday, 21 February 2018 at 14:11:10 UTC, ParticlePeter 
wrote:
> struct Foo(T) {
>   T bar;
>   this(S)(S s) {
>     bar = convert(s);
>   }
> }
>
> auto foo = Foo!int(some_float);
>
>
> this works because S is deduced as typeof(some_float), but how 
> would I instantiate the struct without relying on auto 
> deduction?
>
> Suppose we would have this kind of constructor where auto 
> deduction is not possible:
>
>   this(int n)(float f) {
>     static foreach( i; 0..n) { do_some_ctfe_magic;}
>   }
>
> How to instantiate Foo then?

No can do. The solution is to use a factory function:

struct Foo(T) {
     static Foo create(int n)(float f) {
         Foo result;
         static foreach( i; 0..n) { do_some_ctfe_magic;}
         return result;
     }
}

--
   Simen