Determine if a type if derived from a template parameter

[Basile B.]

On Wednesday, 10 April 2019 at 19:28:38 UTC, Alex wrote:
> e.g.,
>
> class X(T,S)
> {
>    T x;
>    S y;
> }
>
> Somehow determine if x's type is derived from the template 
> parameter.
>
> I doubt D has this capability but it would be nice for certain 
> things. In my reflect library the types must be specified such 
> as Reflect!(X!(int,float)) and ideally I would like to do 
> Reflect!(X!(T,S)) to get generic reflection information. This 
> helps reduce overhead as one could reflect once on the generic 
> type, cache the results, then simply modify the results for 
> specifics.

You can detect a match between a member and a template argument 
but you cant know if the match is a coincidence or on purpose. 
For example:

   class X(T)
   {
       T x;
       int y;
   }

   alias X1 = X!int;

here X1.y matches to T but it's a coincidence.
The problem that you'll be faced to is that the template 
parameters are replaced by the symbol or the type.