delete and __delete not equivalent

[Adam D. Ruppe]

On Friday, 15 January 2021 at 14:38:55 UTC, Steven Schveighoffer 
wrote:
> I'm unsure if deleting from the middle is expected or desired.

Yeah, in my private implementation, I have a sanity check that 
the pointer and the base aren't too far apart. I figured they 
didn't line up due to a capacity cache or similar metadata at the 
beginning of the block (though I didn't prove this) and thus the 
pointers shouldn't be more than like 16 bytes apart and anything 
more than that is suspicious.

So far in my tests that appears to be exactly the case - 16 bytes 
on both 32 and 64 bit.

But while that might be good enough for my barely-documented 
"WARNING: calling this function might break your code" thing, idk 
if that is the right answer for druntime itself.

However if I can prove it is correct, I do think it is reasonable 
to go back to silently doing nothing if the pointers are further 
apart since freeing the whole block from a partial slice is a bit 
iffy in terms of correctness. You wouldn't do that with malloc.