[boost] Re: Unordered associative containers and swap's exception safety

From: David B. Held (dheld_at_[hidden])
Date: 2005-02-11 19:26:11

Daniel James wrote:
> [...]
> 'For unordered associative containers, no swap function throws an 
> exception unless that exception is thrown by the copy constructor or 
> copy assignment operator of the container's Hash or [equality] Pred 
> object (if any).'
> [...]

Frankly, I don't understand why Hash or Pred should be copied
at all during a swap.  If swapping Hash or Pred via std::swap()
would throw, it seems like a no-brainer that the authors of
Hash and Pred should provide a non-throwing swap() which can be
discovered via ADL.  In fact, I don't see any good reason why the
standard shouldn't simply require that Hash and Pred provide a
non-throwing swap() if std::swap() would throw.

Dave