On Wednesday, 2 November 2016 at 05:00:23 UTC, Andrei
Alexandrescu wrote:
In order to make opAssign safe, a language change will be
necessary.
Technically, it should be possible with runtime checks:
https://forum.dlang.org/post/aeeffshzkfjbrejzt...@forum.dlang.org
The checking overheads disappear when -noboundschecks is passed.
The user has to manually copy the RCSlice when necessary for
correct code.
The RCSlice in the link is just a basic proof of concept, using
RCRef for temporary references. It doesn't handle reallocations -
I think to have early diagnostics of potential errors it would
need to have a separate RCRef reference count from the main
count. That would be used to check there are no RCRef references
alive when the main count is one and a reallocation could
potentially occur - e.g. when appending. I think with this
(hypothetical) RCSlice it's bug-prone to allow the user *not* to
make a temporary copy of the RCSlice in this scenario because
errors could depend on unknown runtime behaviour, not showing up
in testing.
I mention this partly because I think this scenario has an impact
on the design of a DIP to address when to automatically add
reference counting bumps - perhaps a @rcbump attribute is
necessary. Otherwise the compiler can't know if an external
function taking an RCString performs an append or not.
