Verifying the arguments of a function with ref parameters?

[jdfgjdf via Digitalmars-d-learn]

On Thursday, 28 July 2016 at 19:19:06 UTC, pineapple wrote:
> Why doesn't this code do what I'd expect it to, and how can I 
> fix it?
>
>     unittest{
>         import std.traits : Parameters;
>         // Works as expected
>         alias dg = int delegate(int value);
>         enum bool dgcallable = 
> is(typeof((){dg(Parameters!dg.init);}));
>         pragma(msg, dgcallable); // Prints true
>         // Doesn't work as expected
>         alias dgref = int delegate(ref int value);
>         enum bool dgrefcallable = 
> is(typeof((){dgref(Parameters!dgref.init);}));
>         pragma(msg, dgrefcallable); // Prints false
>     }
>
> Thanks!

"Parameters!dgref.init" does not yield a reference. The real 
error is not displayed. In a normal context it would be "stuff is 
not callable with...."