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From: Ian Collins <ian-news@hotmail.com>
Newsgroups: comp.lang.c++
Subject: Re: Fast swapping of STL containers
Date: Fri, 24 Jun 2011 23:35:06 +1200
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On 06/24/11 11:25 PM, Kai-Uwe Bux wrote:
> Ian Collins wrote:
>
>> On 06/24/11 10:29 PM, ittium wrote:
>>
>> Please stop snipping attributions, it's rude!
>>
>>>> What difference does the number of calls make?  The operation is either
>>>> efficient, or it isn't.
>>>>
>>> thanks Ian for quick response.
>>> If operation is called limited number of times (e.g. only during
>>> initialization of a process) you can live with it. But if it is called
>>> large number of times and fast response time is required, complexity
>>> is an important criteria before using a routine.
>>
>> How is the library designer to no how often a routine will be called?
>> They will strive to get the best performance and that will be much
>> better than a user will ever get!
>
<snip>
>
> Lessons: (a) sometimes and with some effort, the library designer can not
> only measure how many times the routine will be called but also get an idea
> of the typical arguments; (b) if your particular use case differs from the
> case for which the library was optimized, you can sometimes rather easily
> beat the library implementation.

But not in the cast of an operation such as a container swap which can 
typically be implemented by exchanging some pointers to the internal 
data structure and a few other internal variables.  The user would have 
to perform a copy and erase.

-- 
Ian Collins