"Lemings, Eric B. \(Contr\)" writes:

The semantics of MPL's insert metafunction for an extensible associative sequence is defined as:

"For any Extensible Associative Sequence s, iterator pos in s, and arbitrary type x:

typedef insert::type r;

Semantics: r is concept-identical and equivalent to s, except that at< r, key_type::type >::type is identical to value_type::type."

What happens if the key type of x is already in s?

That's covered by the semantics; it's not a special case. The new value value_type::type is associated with the key key_type::type in r. HTH, -- Dave Abrahams Boost Consulting www.boost-consulting.com