Re: [Boost-users] shared_ptr in API

From: Peter Dimov (pdimov_at_[hidden])
Date: 2006-08-02 18:56:14

Philippe Lambert wrote:
> Hello,
>
> We are a large team of C++ developers, using Boost at large.  We have
> a philosophical issue about shared_ptr usage and I'm looking for
> external inputs.
>
> The 2 clans are opposed about a simple question:  "Should we use
> shared_ptr in the API function signatures of a module (dll or else)".
> Both clan use a lot of Sutter/Meyers/other gurus and authors citation
> to support their view.
>
> 1- Pros:  shared_ptr are everywhere in the current code.  It is the
> best way to prevent resources leaks, it is easy to use, convenient,
> it is mostly safe.  A lot of gurus are saying "use shared_ptr".
> Preventing them in API will means a lot of .get() in the existing
> code.
>
> 2- Cons:  A shared_ptr in the API give the right to the called
> function to keep a copy (virtually permanently) of the object.  It is
> a bad indication in the contract if the function doesn't need to keep
> a copy.  It tell to the user "take care, I may keep a copy of this
> and influence his life cycle". If it is not the case, you should tell
> it in the signature by asking for a const reference or something like
> it.  Also, if the caller have a stack object and want to use an API
> function which ask for a shared_ptr, he will need to create a copy,
> or create a shared_ptr with a deactivated destructor...  It is not a
> beautiful thing, both ways.

Haven't you already answered your own question? If a function needs to keep 
a copy of the pointer to the object, use shared_ptr; otherwise, use a 
reference.