[Dlang-study] [lifetime] Initial thoughts on lifetime management

[Timon Gehr]

On 10/28/2015 04:07 PM, Andrei Alexandrescu wrote:
>
>> How does the compiler lose control with opInc/opDec? It could still fuse
>> them.
>
> Fusing them relies on the compiler knowing the effects are additive
> (three successive opInc()s mean += 3 etc) and also that opInc() and
> opDec() cancel each other. Allowing the user to define them arbitrarily
> prevents the compiler from doing some of these things, or limits what
> the user can do drastically enough to just mandate one implementation.

I disagree that it limits the user drastically enough to just mandate 
one implementation. E.g. (for whatever reason) a user might want to use 
reference counting with an allocator that does not allow individual 
deallocation of objects. (It is then sufficient to have only a single 
reference count, for the allocator itself.)

>
>> How to specify the allocator for a @rc class?
>
> I don't know, it's a good topic for discussion. Ideas?

It could be a special member that is either an alias or a reference to 
an allocator which is automatically filled by the typed part of 
std.allocator. Alternatively, one could make the references fatter and 
have an additional argument to (an overload of) opDec.