Re: [boost] stack-allocated STL-containers

Subject: Re: [boost] stack-allocated STL-containers
From: Stefan Strasser (strasser_at_[hidden])
Date: 2009-08-13 20:46:50

Am Friday 14 August 2009 00:24:54 schrieb Mathias Gaunard:
> > the vector operates on the stack as long as there is enough space, and
> > moves to the heap afterwards.
> > in most cases there is no dynamic allocation.
>
> An implementation is free to consider any instance of an allocator with
> the same arguments passed to the constructor as equal, IIRC.
>
> Does your allocator suffer from this issue?

I don't think so. the allocator doesn't have any state except a constant 
pointer to "buffer"(see exmaple above), so multiple copies of the same 
allocator can be used simultaniously.
the only c++ standard requirement it can't fulfil is a default constructor. 
I'm not sure why that is needed though. but the standard says that 
Allocator() must be a valid expression.

> Also, is the container still copyable properly?

yes. the only issue that might arise is that the buffer on the stack could go 
out of scope before the vector has, as a result of swap()ing the contents of 
the vector into another vector with a longer lifetime.
but I don't think that's a violation of the standard because that is also true 
for other allocators, e.g. pool allocators.

Am Friday 14 August 2009 00:00:37 schrieb Christian Schladetsch:
> Two immediate issues are alignment and the fact that you are using a
> stateful allocator.

do you consider a constant pointer "stateful", and why is that a problem?