On 3/1/18 2:04 PM, Jonathan M Davis wrote:
On Thursday, March 01, 2018 10:55:34 Steven Schveighoffer via Digitalmars-d-
learn wrote:
It should really say that it's up to the GC implementation whether it's UB
or not.
Well, that arguably makes it UB in general then, because it can't be relied
on. By putting restrictions on the GC in general based on what types of GCs
theoretically could be used, it makes it so that D code in general could
theoretically work with any GC that fits the bill, whereas if the rules of
what was allowed changed depending on the GC being used, what was valid D
would effectively change depending on the GC.
There are a few in there, which I think are over-the-top. Such as "don't
cast a pointer to a non-pointer", or "Do not take advantage of alignment
of pointers to store bit flags in the low order bits". I can't conceive
of any GC that would have fits with either of these things without
breaking pretty much everything. While I can't conceive of it, it
doesn't mean there isn't a reason for it. But clearly the reason isn't
currently implemented.
-Steve
