Re: [Boost-users] custom allocators Re:pool_alloc

Subject: Re: [Boost-users] custom allocators Re:pool_alloc
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2010-03-19 18:47:33

AMDG

Scott McMurray wrote:
> On 19 March 2010 14:02, Eric Whitcombe <ericwsf_at_[hidden]> wrote:
>   
>> Sorry, if this is a little late to be helpful but I thought I'd add this for
>> historical purposes for anyone looking at this thread to deal with their own
>> problem. All STL containers use allocators to allocate and initialize the
>> memory to store the _elements_ in the container not the node structure. The
>> containers definition of the data structures that support the implentation
>> details are purely internal. The allocator interface is paramterized on the
>> type of the container element.
>>
>>     
>
> On that note, does anyone know why allocators are parametrised at all?
>   

Probably because the original idea was just to allocate
the type passed.  Then someone realized that doesn't work
for node-based containers and said, ah, we'll just add rebind.

> Since std::vector is the only container that actually allocates from
> passed-in allocator, it seems like it would have been simpler to just
> use member templates in a non-templated allocator class.
>   

Well, you still need the pointer, reference, etc. typedefs, somehow.

> (Parametrised allocators also mean that nested containers have
> exponential space requirements for their names, which actually crashed
> my compiler once when I tried to make a deeply-nested container
> structure in some recursive-slowdown experiments.)

Yep.  Probably no one thought ot this until it too late to
do anything about it.

In Christ,
Steven Watanabe