On Tuesday, 30 September 2014 at 15:46:54 UTC, Steven
Schveighoffer wrote:
So I made the call to put it at the beginning of the block,
which obviously doesn't change, and offset everything by 16
bytes to maintain alignment.
It may very well be that we can put it at the end of the block
instead, and you can probably do so without much effort in the
runtime (everything uses CTFE functions to calculate padding
and location of the capacity). It has been such a long time
since I did that, I'm not very sure of all the reasons not to
do it. A look through the mailing list archives might be useful.
Yes, a lot of this is an artifact of the relatively simplistic
manner that the current GC tracks memory. If large blocks had a
header, for example, then this could theoretically live there and
not cause any problems. As we move towards supporting precise
scanning, the GC will need to be aware of the types of data it
holds, and so some portion of the array appendability strategy
should probably migrate into the GC. A redefinition of the GC
interface is many years overdue. This just needs to be
considered when it happens.
