Re: 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.