Issue Turning Template into Variadic Template

[jmh530 via Digitalmars-d-learn]

On Wednesday, 30 March 2016 at 18:56:29 UTC, H. S. Teoh wrote:
>
> Does this do what you want?
>

Okay, I've looked at this a bit more thoroughly and it works 
perfectly (perhaps with a better name put in phobos?).

If I'm understanding this correctly, the ImplType creates the 
correct type signature for the output and then conditionalOnly 
puts the right value in.

One thing that is confusing is that when I create a new function 
that adjusts conditionalOnly to just return y instead of fun(y), 
then I get an error about returning a tuple. I'm like, where did 
I use a tuple. I guess related to
https://issues.dlang.org/show_bug.cgi?id=15436