Re: [Boost-users] Lack of release() in scoped_ptr and scoped_array

From: Rene Rivera (grafikrobot_at_[hidden])
Date: 2006-08-02 15:34:00

Milutin Jovanovic wrote:
> I finally decided to switch to boost from my own implementation of some 
> helper classes, and I noticed that scoped_ptr and scoped_array in boost lack 
> the release method(). I had to fall back to std::auto_ptr.
> 
> However, this seems like such a basic and fundamental problem that I have 
> started to fear that I am missing something obvious... The usage I got used 
> to was something like this:
> 
> {
>     scoped_ptr<A> temp( new A() );
>     verify( temp.get() ); // might throw
>     store_in_a_very_special_place( temp.get() ); // might throw; and I 
> should keep ownership if thrown
>     temp.release();
> }
> 
> I though this was good practice to make code exception safe. Sure I could do 
> it with try-catch but that gets messy if I allocate multiple instances etc.

Try writing it as:

{
     shared_ptr<A> temp( new A() );
     verify( temp ); // might throw
     store_in_a_very_special_place( temp ); // might throw; and I
should keep ownership if thrown
}

It's less code and it's safer. But if you must use scoped_ptr another 
alternative would be:

{
     scoped_ptr<A> temp( new A() );
     verify( *temp ); // might throw
     store_in_a_very_special_place( *temp ); // might throw; and I
should keep ownership if thrown
}

> So the question is:
> 
> 1) is there something wrong with the concept of release()?
> 2) if release() is not evil, is there any other reason why is it not in 
> boost::scoped_*?

See the FAQ for this at the bottom of the scoped_ptr docs 
<http://boost.org/libs/smart_ptr/scoped_ptr.htm>.

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