Re: [Boost-users] Overloading operators with multi index container?

Paul Dovydaitis writes:

We are using a multi index container to store some data indexed both by a text key and by a timestamp. [...]   To do this, we tried to overload operator< in the following way:   bool MyTransaction::operator<(const Transaction & rhs) const {     const std::time_t WINDOW = 2;            if (getHashKey() == rhs.getHashKey()) {                   if ((epochTime() - WINDOW) <= rhs.epochTime() &&                 (epochTime() + WINDOW) >= rhs.epochTime())         {             return false;         } else {             return (epochTime() < rhs.epochTime());         }     } else {         return (getHashKey() < rhs.getHashKey());     } }

This less-than operator is ill-defined according to the semantics expected by Boost.MultiIndex indexed indices (as well as STL associative containers and a number of stdlib algorithms). In particular the operator must implement a strict weak ordering: http://cpp-next.com/archive/2010/02/order-i-say/ Among other, a strict weak ordering has the property that "equivalence" defined as x~y := !(x