[boost] [config] gcc and <unordered_set> vs <ext/hash_set>

Subject: [boost] [config] gcc and <unordered_set> vs <ext/hash_set>
From: John Maddock (john_at_[hidden])
Date: 2008-12-16 12:14:02

Folks, Dave A. asked for a config macro to detect the presence of std 
conforming <unordered_set> and <unordered_map>.

However, I've run into an unexpected issue: it appears that with gcc-4.3.x 
you cannot include both <unordered_set> and <ext/hash_set> as attempting to 
do so leads to endless errors inside the <ext/*> headers :-(

Including either one of the headers is just fine though.

So... how should we handled this?  Not define BOOST_HAS_HASH when 
<unordered_set> *is* available?

As far as I can tell the only library effected by this change would be 
Boost.Serialization which would lose has_set support in gcc's c++0x mode. 
How do folks feel about that?

Regards, John.