Reference counted containers prototype

[Martin Nowak]

On Mon, 26 Dec 2011 18:25:10 +0100, Andrei Alexandrescu  
<SeeWebsiteForEmail at erdani.org> 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

     // "empty" object intended for static and immutable methods when
     // the data pointer is null. It won't be modified. We assume the
     // empty object is equivalent to a null stored pointer.
     private static immutable T _empty;

I don't see much need for this.
Instances without identity are rarely useful, i.e. you will mostly  
initialize
them to a particular value before using them.
I could think of some strategy constructs being used with templates,
but then you would not wrap them in RefCounted in the first place.

Of course RefCounted should not create a value when accessing static  
members.