Understand signature of opOpAssign in std/complex.d

[Adam D. Ruppe]

On Monday, 11 November 2019 at 16:59:57 UTC, Q. Schroll wrote:
> What's the difference of
>     is(C R == Complex!R)
> to
>     is(C == Complex!R, R)
> then?

Nothing, they do the same thing.

(I'm of the opinion that the first one should actually be illegal 
- I thought it was until I checked for this thread - since it is 
weird. The general rule is placeholders need to be defined after 
the pattern, not before. The `C R == X` thing usually defines R 
to be an alias of something that already exists - maybe C itself, 
maybe a specialization of X like __parameters - but meh it did 
work here so weird and as far as I can tell they are identical.)