PATCH: use construct and destroy from user-provided allocators

[Matt Austern <austern at apple dot com>]

As discussed earlier, this patch makes STL containers use their 
allocators to construct and destroy elements.  (i.e. using the 
Allocator::construct() and Allocator::destroy() member functions.)  
Test cases included.

There are a lot of lines of changes, but it's really pretty 
straighforward: I define versions of the uninitialized_* functions, and 
_Destroy, that take allocators as arguments.  I overload them so that 
when the allocator is std::allocator() they behave the same way as the 
old versions did.

Two things to notice about this patch.
1. There is a cost to doing this.  Right now, there are cases where we 
optimize initialization to memset/memmove and there are cases where we 
optimize destruction to nothing. If we're committing to using 
construct/destroy for user-provided allocators, that means we can only 
do these optimizations for std::allocator.  I think this is an 
acceptable cost, since people who provide their own allocators ought to 
have a reason for doing it, but it is a cost.
2. I'm only using construct() and destroy() for containers' elements.  
I think that's all the standard demands, and it's probably all that 
users really want.  Conceivably we should also be using construct() and 
destroy() for other things we allocate (pointers, nodes, etc) but we 
can leave that for another day, if ever.

OK to commit to mainline?

			--Matt

Attachment: construct-patch.txt
Description: Text document