Let's improve D's exceptions

[Steven Schveighoffer via Digitalmars-d]

On 5/18/15 8:20 AM, Atila Neves wrote:
> One thing I like about `enforce` is that the program's run-time checks
> become positive instead of negative statements which I think is a lot
> more readable. i.e.
>
>      enforce(foo && bar > 4, "...");
>
> instead of
>
>     if(!foo || bar <=3) throw new Exception("...");

Yes, but that's a minor nuisance. I often do not rewrite conditions by 
distributing the negation to avoid this problem. In that case, the 
"operation" becomes basically:

if(!(...))

We could introduce a new 'when' keyword:

when(...)

joking, joking!!! don't start flaming :)

Alternatively, we could fix lazy parameters so they don't disable 
inlining (though the weight carried by enforce is so minor, I still 
don't think it's worth having).

-Steve