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From: Jochen Eisinger on 16 Jan 2008 18:11
Hi,

if I'm not mistaken, the compare parameter of the std::set template has
to fulfill the "strict weak ordering" requirement. In contrast to a
"total ordering", two objects might just not be comparable by a strict
weak ordering, i.e. neither x < y nor y < x although x != y.

So using a "strict weak ordering", std::set can't determine whether an
element is already in the set or not, just whether an element of the
same class wrt. the compare parameter is already in the set.

In fact, if you instantiate std::set as implemented with gcc with a
not-total ordering, you can't insert two different elements, which
cannot be ordered.

So my question is: should the compare object actually fulfill a total
ordering requirement, or should a set be seen as a container containing
one representant per equivalence class?

regards
-- jochen

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