Re: [boost] [circular_buffer] some comments and suggestions

From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2008-01-21 06:58:10

Neil Groves skrev:
> Hi!
> 
> I agree with most of the comments from Thorsten. I do however disagree with
> point 1. The allocation in the constructor allows zero allocation in the
> subsequent push calls. Often a circular_buffer is used in tight loops of
> push operations. I would not want the additional overhead of the allocation
> check. With types with no-throw guarantee copy constructors I also would not
> want the additional possibility of an exception thrown from the push
> operation. I would not use this class if the push operation had this
> additional overhead.

I don't see how you get into the troubles you mention. I don't want 
push_back() to regrow, but neither does it have to: simply can reserve() 
prior to use. Otherwise you get whetever push_back() does on an empty 
buffer (either we say as a precondition that it is not empty, or we 
allow it to do nothing at all).

-Thorsten

> On Jan 21, 2008 10:40 AM, Thorsten Ottosen <thorsten.ottosen_at_[hidden]>
> wrote:
> 
>> Hi Jan,
>>
>> #1
>> I was browsing through the docs in trunk. First I noticed that the
>> default constructor has the follwoing postcondition:
>>
>>   capacity() == max_size() && size() == 0
>>
>> I find that somewhat unfortunate that it allocates a huge amount of
>> memory. It seems to me that it is too easy to do that by coincidence.
>> The usual rule for std containers is to never allocate by default and
>> anticipate a call to reserve() or the first element. It also seems to me
>> that this will create problems when the container is used in containers
>> that might use default construction.