🚀 go-pugleaf

In article <477o7e$5pd@info.uci.kun.nl> Marian Hellema <marian@atcmp.nl> writes:

> The ObjectSpace documentation states:
> "All the items that are stored in associative containers must be
> comparable using == and <"> 
> I have not been able to find a confirmation for this rule in the
> standard working paper. Can someone clear this up for me?


All of the associative containers in the STL require that a comparison
function be defined for items in the container, but it does not
necessarily have to use operator <.  (See section 23.3 of the draft
standard.)  One of the template parameters of the associative
containers is a comparison function object used to compare items in
the container.  By default the comparison object is less<Key>, meaning
that it uses operator <, but you may provide a different type if you
want to store objects for which operator < is undefined.

(Note, incidentally, that you may pass a comparison object in the
container's constructor: each container may have its own comparison
object.  This argument defaults to Compare(), which, again, defaults
to less<Key>().)

It's still true that you must define an ordering for whatever type
you're putting in the container; you simply aren't required to use
operator <.  Associative containers that you can use for unordered
keys would also be useful, but a proposal to add them to the standard
was rejected.  

-- 
  Matt Austern                             He showed his lower teeth.  "We 
  matt@physics.berkeley.edu                all have flaws," he said, "and 
  http://dogbert.lbl.gov/~matt             mine is being wicked."

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