Re: [boost] [ptr_container] Questionable strong guarantee of ptr_map::insert()

Subject: Re: [boost] [ptr_container] Questionable strong guarantee of ptr_map::insert()
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-08-25 09:06:07

Nevin ":-]" Liber wrote:
> 2009/8/24 Jeffrey Bosboom <jbosboom_at_[hidden]>
>
> > For the record, if the argument was an auto_ptr&, I would expect the
> > auto_ptr to still own the resource if an exception was thrown, although I
> > don't know how to implement it (moving back into the auto_ptr might throw
> > too).
>
>
> The implementation is actually fairly simple.   In psuedocode:
>
> internal_insert(Iterator position, T* p)
> {
>     // insert p into the container; throw on failure
> }
>
> insert(Iterator position, auto_ptr<T>& ap)
> {
>     internal_insert(position, ap.get());
>     ap.release();
> }
>
> insert(Iterator position, T* p)
> {
>     auto_ptr<T> ap(p);
>     insert(position, ap);
> }

Reasonable

> While I do understand how "copy" semantics work for auto_ptrs, when I see an
> auto_ptr as a (sink) parameter to a function, my expectation is that either
> the callee takes ownership of the underlying object, or if it fails, that I
> as the caller retain ownership.  The details are, of course, that one passes
> the auto_ptr by non-const reference to any function that might fail.

You might argue that the function should take an auto_ptr by reference, but as written, it does what it ought.

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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