Subject: Re: [boost] Stack-based vector container
From: Thorsten Ottosen (nesotto_at_[hidden])
Date: 2011-01-23 19:11:46
Den 24-01-2011 00:59, Emil Dotchevski skrev:
> On Sun, Jan 23, 2011 at 1:01 PM, Thorsten Ottosen<nesotto_at_[hidden]> wrote:
>> As for the conjectured extra indirection, then I'm not sure it can become
>> any major performance problem, nor do I see how one can avoid it when we
>> need to go for the heap in certain cases.
> Clearly the extra indirection is the only potential problem, otherwise
> a stack-based vector implementation could probably be replaced by a
> stack-based std::vector allocator.
> However, the cost of the extra indirection is platform-dependent and
> difficult to measure in the abstract. In my experience, most cases
> when someone has complained about inefficiencies in std::vector boil
> down to incorrect use:
> - not using reserve();
> - calling push_back()/insert() in a loop (which is inefficient even
> with reserve);
> - iterating by redundantly calling end() each time;
can be hoisted for vector, but not for most other containers.
> - using operator for sequential access to the elements.
> So the only meaningful way to evaluate the benefits of a std::vector
> alternative is to discuss specific use cases, considering other
> alternatives as well.
A stack-based allocator will work in C++0x, and probably works ok in
C++03. In any case, the array needs to be created externally to the
class which is somewhat more inconvenient, especially if you need to
copy the vector around.
But anyway, I agree on your requirements for a good analysis.
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