[boost] Re: Should std::allocator::rebind be used with std::map?

From: Andreas Huber (ah2003_at_[hidden])
Date: 2004-05-20 09:31:05

Hello Joaquín,

>> which should work with just about any implementation of the std
>> library, as long as the used container is a list, (multi)set or
>> (multi)map.
>
> Well, this is not generally true. In most cases the thing will work,
> but consider for example the following:
>
> #include <list>
>
> typedef std::list<
>   int,
>   std::allocator<double>
>> my_list;
>
> int main()
> {
>   my_list l;
>   my_list::reference e=*l.begin(); //error here
> }
>
> This actually fails to compile in CW 9.3 (it works for some other
> environments). Strictly speaking, CW 9.3 is right to not compile the
> snippet, as my_list::reference is double& instead of int&. The
> fact that it compiles for other stdlibs is sheer luck.

Ok, I missed this. I think your snippet should not compile on *any* std
conforming implementation as the standard clearly says that the type of
std::list< ..., Allocator >::reference must be equal to
Allocator::reference.

[snip]
>
http://www.boost-consulting.com/boost/boost/multi_index/detail/allocator.hpp
>
> (rebind_to utility) for an example of what can be done to overcome
> the problem.

Hmmm, any chance this will make it into boost::detail namespace instead of
boost::multi_index::detail, for V1.32? That'd be great because I could then
reuse it in boost::fsm. I guess other libraries could benefit from this
also.

> Hope this helps,

Yes, very. Thanks!

Regards,

Andreas