Warn about using the GC

[Richard (Rikki) Andrew Cattermole]

On 15/01/2024 3:03 AM, Nickolay Bukreyev wrote:
>     This makes it so things like |opApply|, only need one overload, not
>     say 24 of them to handle all the different combinations of attributes.
> 
> Just curious, why 24? +/- nothrow, +/- pure, +/- @nogc, 
> @safe/@system—that’s /only/ 16. You can cut it down to 8 if you always 
> require @safe (callers will have to provide a @trusted callback).

I ran a permutation on it a couple of days ago. Might not be too accurate.

But it is still a significantly larger number than 1 ;)