Re: [boost] Stack-based vector container

Subject: Re: [boost] Stack-based vector container
From: Bo Persson (bop_at_[hidden])
Date: 2011-01-17 12:37:26

Domagoj Saric wrote:
> "David Bergman" <David.Bergman_at_[hidden]> wrote in message
> news:FF46F967-E45E-4188-9976-6090F2054A51_at_bergmangupta.com...
>> What you are doing here is to mix two (presumably...) orthogonal
>> aspects, in that you bake in the allocation policy in the vector
>> interface. In fact, a "static allocator" to be used in cases like 
>> std::vector
>> was discussed
>> at length on this list a year ago (or was it two years?)
>
> This is not quite the same, i.e. std::vector is 'too' generic so it
> would still incur overhead compared to a simple
> "stack-buffer-with-an-end-pointer": it contains (and maintains)
> three pointers (or std::size_ts) begin, end and "reserved end" as
> opposed to only an end pointer/std::size_t + it is designed around
> the 'idea' of "fallible allocation", that is it expects allocation
> requests to possibly throw so in some cases/member functions
> implementations have to use guard objects and/or explicit exception
> handling (which the optimizer may or may not be able to remove) ...
> and this same problem might obfuscate the code (for the compiler)
> enough so that the optimizer might not be able to detect that a
> 'std::vector with a static allocator' does not throw and cause it
> to still emit EH code/unwind funclets (for surrounding/calling
> code)...

If you have a fixed size vector, you cannot call functions that might 
require a reallocation (push_back is out of the question). So the 
compiler doesn't have to generate those functions at all.

Bo Persson