ref returns and properties

[Jacob Carlborg]

Andrei Alexandrescu wrote:
> Michiel Helvensteijn wrote:
>> Andrei Alexandrescu wrote:
>>
>>> void move(ref T src, ref T dst);
>>> void swap(ref T lhs, ref T rhs);
>>>
>>> ...
>>>
>>> But if "prop" is a property with get and set, everything falls apart.
>>> Properties effectively hide the address of the actual data and only
>>> traffic in values. That's often good (and sometimes even the only
>>> possibility in the case of properties computed on-the-fly), but this
>>> abstraction effectively makes resource-conserving move and swap
>>> impossible.
>>>
>>> ...
>>>
>>> What to do? I'd like to refine the notion of property such that moving
>>> properties around is possible, without, however, complicating their
>>> interface too much.
>>
>> I posted a possible solution to this (I think) in the last properties
>> thread. I was thinking that properties might be equiped with extra member
>> functions. One advantage is that you might get more efficiency. I 
>> think you
>> just named another.
>>
>> class Host
>> {
>>      property prop
>>      {
>>          T get() { ... }
>>          void set(T value) { ... }
>>          void move(ref T dst) { ... }
>>          void swap(ref T rhs) { ... }
>>      }
>> }
> 
> But these are too many. These should suffice:
> 
> class Host
> {
>      property prop
>      {
>          T get();
>          void acquire(ref T value) { ... }
>          void release(ref T value) { ... }
>      }
> }
> 
> set() can be implemented as acquire from a copy, and swap can be 
> implemented by calls to acquire and release. Technically, get() could be 
> also implemented with acquire and release, but that's too intensive for 
> most types.
> 
> The problem I'm seeing is that most people won't want to go through the 
> trouble of implementing three functions for one property.
> 
> 
> Andrei
> 

What about this:

class Host
{
      property acquire release prop
      {
          T get();
      }
}

And then the compiler will automatically created the "acquire" and 
"release" methods.

There could also be what I would like to call "property shortcuts" (ruby 
calls this attributes) like this:

class Host
{
      get acquire release T prop;
      get set T prop2;
}