A Huge Bummer When Using alias this

[Meta via Digitalmars-d]

On Thursday, 24 March 2016 at 21:26:00 UTC, Jack Stouffer wrote:
> alias this is only useful when not using any function that 
> relies on the template constraints in std.traits.
>
> For example
>
> import std.traits;
>
> void someFunc(N)(N val) if (isNumeric!N)
> {
>     int b = val;
> }
>
> void main()
> {
>     import std.typecons;
>     Nullable!int a = 42;
>
>     someFunc(a);
> }
>
> $ dmd test.d
> test.d(13): Error: template someFunc cannot deduce function 
> from argument types !()(Nullable!(int))
>
> Removing the template constraint makes it compile and run just 
> fine. What's a good work around for these types of issues?

It has been brought up quite a few times before and if I recall 
Andrei wasn't all that concerned. For what reason I'm not sure, 
as alias this is supposed to introduce a subtype yet it clearly 
isn't because template constraints will fail when they shouldn't. 
Basically there's no workaround aside from defining your own 
isNumeric and forwarding to std.traits.isNumeric.