Re: [boost] [utility] new auto_buffer class --- RFC

Subject: Re: [boost] [utility] new auto_buffer class --- RFC
From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2009-03-14 04:42:46

David Abrahams skrev:
> 
> On Mar 3, 2009, at 1:45 AM, Thorsten Ottosen wrote:
> 
>> Steven Watanabe skrev:
>>> AMDG
>>> Thorsten Ottosen wrote:
>>>>> Certainly swap should be provided somehow; a fast-as-possible swap is
>>>>> not otherwise possible since the user can't get at the buffer pointer.
>>>>> boost::array supports swap, and yours should be at least as fast as
>>>>> that.  On that precedent I'd say you should support swap() under that
>>>>> name.  Has anyone ever complained about the deceptive slowness of
>>>>> boost::array's swap?
>>>>
>>>> I don't know. I just stay clear of it. The point is that we don't want
>>>> inexperienced users to use an O(n) swap accidently.
>>> Please define n.
>>
>> n would be c.size()
> 
> I'm sorry, I know this will sound harsh, but I don't know how else to 
> say it: we went down this road with ptr_container, and should not repeat 
> that mistake.  

ptr_containers have been copy-constrictible, and assignable is some 
releases now.

>The instinct to protect naive users from performance 
> pitfalls by leaving out fundamental operations (swap in this case; 
> assignment and copy in the case of ptr_container) is just wrong.  That's 
> especially true when the implementations would NOT violate the 
> efficiency guarantees required by the concepts.

I have provided a swap(), see the thread "[utility] auto_buffer v2".
But a linear size() can be problematic, so can a linear swap().

> Let me also point out that std::array will support swap for C++0x (by 
> swapping individual elements).

Ok. Somebody should add it to boost::array then.

-Thorsten