Object oriented languages generally include some form of
dynamic dispatch;
that is, in the absence of precise compile-time type information, they
perform a run-time selection of the appropriate function body (or
method) from a set of candidates.
Existing single-dispatch languages restrict dynamic dispatch to the
object receiving the message.
Such languages exhibit a conflict between the goals of providing an
extensible a set of types and providing an extensible the set of operations that
can be performed on these types.
We show that this conflict is a consequence of the restriction of
dynamic dispatch to the receiver object.
We also demonstrate that this conflict can be resolved by introducing
a generalized form of single dispatch (thus avoiding the complexity of
multiple dispatch).
On this evidence, we argue that dispatch technique should be
decoupled from membership in a class and access to its representation.
