Re: [boost] Performance comparison between ptr_vectorandvector<cow_ptr<Shape> >, vector<copy_ptr<Shape> >

From: Thorsten Ottosen (tottosen_at_[hidden])
Date: 2006-01-06 12:31:38

David Maisonave wrote:
> "Sam Partington" <sam.partington_at_[hidden]> wrote in message
> news:<546fdb840601060205w76ed8be9n2bf73c4323c78c20_at_[hidden]>...

>>I don't agree with that.  The clone concept is a well established 
>>idiom for polymorphic types.  Sure missing out a clone _does_ lead to 
>>slicing, but that is understood, and as Thorsten says we can help 
>>check for that with an assert.  We  can only help the user to get it 
>>write, we can't do it all for them.
>>
> 
> 
> The cow_ptr and the copy_ptr can use the same assert code to catch
> slicing.
> The assert logic can be placed in the constructor of the cow_ptr and
> copy_ptr.
> This would make it easier to catch slicing in the cow_ptr/copw_ptr
> *than* it would be in the boost pointer containers.
> That's because in the boost pointer containers you would only catch
> slicing via assert if and when the object is clone.
> If the object never gets clone during testing, you would never catch the
> slicing.
 >
 >
> 
> With cow_ptr/copy_ptr the slicing would be caught when the object gets
> instantiated.
> So you have a much higher probability of catching slicing using the
> cow_ptr clone method, *than* you would using the boost pointer container
> method.

I'm not sure I fully understand how the detection mechanism would work 
in your cow_ptr.

Nevertheless, as soon as the object is outside
a cow_ptr might be sliced. That's reason enough not to allow it.

-Thorsten