Re: [Boost-users] shared_ptr<> null deleter

From: Noah Roberts (roberts.noah_at_[hidden])
Date: 2008-05-16 18:13:11

Marshall Clow wrote:
> At 2:37 PM -0500 5/16/08, Nevin \":-]\" Liber wrote:
>> 2008/5/16 Kevin Martin <kev82_at_[hidden]>:
>>>  My problem is module interfaces. I have a module (set of classes) that
>>>  solve a problem, and they require data. They don't care whether that
>>>  data is on the heap, the stack, or the moon. They just want a pointer
>>>  to it. In this case it is arguable that the pointers passed shouldn't
>>>  be smart pointers at all, just normal pointers.
>> My general rule of thumb is that if mucking with ownership or
>> lifetime, pass a smart pointer.  If not, pass a raw pointer.
> 
> A brief addenda (from my rules of thumb) for non-ownership cases:
> 	* If the parameter is optional, pass a raw pointer, and the 
> callee should
> expect a NULL pointer.
> 	* If the parameter is not optional, pass a reference.

I don't like this idea.  You are creating a dependency on the fact that 
the called function will NOT keep a copy - or you are insisting that the 
object in question implement the shared_from_this model.  If you later 
decide that it would be prudent for the function or object in question 
to create or pass a kept copy of this object then you'll have to change 
the signature of the function and then each and every call to it (to 
remove get() calls).

So while I can see some possible enforcement advantages to this in the 
rare case, I certainly wouldn't use it as a general rule of thumb.  I 
can't count the number of times someone has assumed that nobody would 
need a copy of something and then requirements changing dictated that 
someone did.