Re: [boost] [singleton] Design questions

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2008-01-18 15:46:02

Peter Dimov wrote:
> Tobias Schwinger:
> 
>> Peter Dimov wrote:
>>> What is the reason to prefer the current instance/lease formulation 
>>> instead
>>> of
>>>
>>>     typedef ... instance_type;
>>>     instance_type instance(); // automatically serves as a lease
>>>
>>> ?
>> As we can't expose the instance when automatic locking is done, it is
>> supposed to provide a means to not have to access the instance directly.
> 
> I'm not sure what this reformulation cannot do that the original can. An 
> ordinary singleton can define instance_type as T*. A synchronized singleton 
> can define instance_type as the moral equivalent of shared_ptr<T> (with a 
> hidden unlocking deleter). What am I missing? 
> 

It was one goal to enforce client code not to make any assumptions about 
the type of the pointer.
The reason was easy migration from an unsynchronized to a synchronized 
scenario by enforcing threading-agnostic client code. Further, I found

     'T::instance->foo()'

syntacticly nicer than

     'T::instance()->foo()'

or

     'T::instance().foo()'

.

Regards,
Tobias