Somewhat like the polychromatic horse in The Wizard of Oz movie, the associative containers are creatures of a different color. True, they share many characteristics with the sequence containers, but they differ in a number of fundamental ways. For example, they automatically keep themselves sorted; they view their contents through the lens of equivalence instead of equality;
maps reject duplicate entries; and
multimaps generally ignore half of each object they contain. Yes, the associative containers are containers, but if you’ll excuse my likening
strings to Kansas, we are definitely not in Kansas any more.
In the Items that follow, I explain the critical notion of equivalence, ...