templatized delegate

[Alex via Digitalmars-d-learn]

On Tuesday, 23 May 2017 at 18:14:34 UTC, ag0aep6g wrote:
> Something like this:
>
> ----
> import core.vararg;
> import std.meta: AliasSeq, staticMap;
> import std.traits: isCopyable;
>
> struct A
> {
>     void delegate(...) dg;
>     auto fun(T, U ...)(T t, auto ref U u)
>     {
>         template UncopyableToPointer(T)
>         {
>             static if (!isCopyable!T) alias UncopyableToPointer 
> = T*;
>             else alias UncopyableToPointer = T;
>         }
>         alias U2 = staticMap!(UncopyableToPointer, U);
>
>         U2 u2;
>         foreach (i, E; U)
>         {
>             static if (!isCopyable!E) u2[i] = &u[i];
>             else u2[i] = u[i];
>         }
>
>         return dg(t, u2);
>     }
> }
>
> struct SomeStructThatIsNotCopyable
> {
>     @disable this(this);
> }
>
> void main()
> {
>     void dlg(...)
>     {
>         import std.stdio;
>         foreach (i, t; _arguments)
>         {
>             foreach (T; AliasSeq!(int, string,
>                 SomeStructThatIsNotCopyable*))
>             {
>                 if (t == typeid(T))
>                 {
>                     static if (is(T : U*, U) && !isCopyable!U)
>                     {
>                         write("uncopyable type");
>                     }
>                     else write(_argptr.va_arg!T);
>                 }
>             }
>             /* otherwise: don't know how to handle the type */
>             write(" ");
>         }
>         writeln();
>     }
>
>     auto a = A(&dlg);
>     SomeStructThatIsNotCopyable s;
>     a.fun(5, "a", /* by ref: */ s, /* or by pointer: */ &s);
> }
> ----
>
> That's not exactly pretty, of course. Both A.fun and the 
> delegate are quite complicated. But it might be workable, if 
> run-time variadics are acceptable.
>
> I wouldn't be surprised if the problem can be solved more 
> elegantly. But I don't see how at the moment.

That's cool :)
but anyway, even if I have such params, there are not much of 
them, so it just a minor semantic issue to explicitely name them 
and their types instead of showing, that they are passed but not 
used inside dlg.
And thanks a lot to all for great ideas :)