Chris, it clearly states in your paper that you referenced, in section 4.1,
that he is assuming the erasure of the equal-allocator assumption. Checking the C++ standard, section 20.1.6, you will quickly see that the equal-allocator assumption is still in place under the current standard. Thus the techniques mentioned in that paper are non-portable. I will be the first to say that this is stupid and makes lots of problems, but it is there and there's nothing we can do.
But looking forward, the draft's std:Allocator concept makes no such requirements - only that allocators are equality comparable. There also seems to be a number of questions about what happens when you copy or move an allocator, which implies to me that stateless allocators are no longer required to be the norm. But that's looking forward, not necessarily what's portable now. True, but that paper seriously breaks things anyway -- it adds more methods
to allocator (via a versioning method) which must then be used by the containers to get any benefit. By the time you have required those non-standards things, it's probably not unreasonable to also require proper support for stateful allocators.
Good points. Maybe it's time to start drafting a Boost.Allocator library with advanced allocator concepts :) Andrew Sutton andrew.n.sutton@gmail.com