On Monday, 26 December 2011 at 17:25:12 UTC, Andrei Alexandrescu
wrote:
Hello,
I've been playing with a new approach to reference counting, in
particular for the containers library.
A small prototype is at http://pastebin.com/WnSQY1Jw. The
prototype features a simple doubly-linked list implementation
DListImpl. That is not supposed to be manipulated directly (or
it might, in case the user wants a simple garbage collected
implementation - this is a point in the discussion).
DListImpl has only a couple of primitives implemented. The only
interesting points that it tries to make are:
(a) the presence of the dispose() primitive, which deallocates
all memory and brings the object back to its .init state
(b) the presence of the dup() primitive, which creates a
full-blown duplicate of the object.
The interesting part of the sample is RefImpl, which has a
couple of quite interesting details:
(a) All interaction with the held object is done via
opDispatch. In fact opDispatch can be engineered to statically
enforce no reference to the held object escapes.
(b) A const/immutable call against a non-existing is silently
converted into a call against a default-initialized object.
(c) If a call works and returns the same type for a non-const
and a const object, then the const version is preferred. This
is to reduce the number of calls to ensureUnique().
Destroy.
Andrei
Maybe the fact that the container is duplicated on opDispatch
call time and not on assignment time could be confusing to at
least developers coming from c++. It does benefit from lazy
duplication by doing it this way which might justify it.
Otherwise it seems good.
/Jonas
