These classes extend the basic class "function" when
functions are to be stored and used as method definitions.
The action of setting a method by a call to setMethod creates an object of this class. It's
unwise to create them directly.
The class "SealedMethodDefinition" is created by a call to
setMethod with argument sealed = TRUE. It has
the same representation as "MethodDefinition".
.Data:Object of class "function"; the data
part of the definition.
target:Object of class "signature"; the
signature for which the method was wanted.
defined:Object of class "signature"; the
signature for which a method was found. If the method was
inherited, this will not be identical to target.
generic:Object of class "character"; the function
for which the method was created.
Class "function", from data part.
Class "PossibleMethod", directly.
Class "OptionalMethods", by class "function".
Method definition objects are functions with additional information
defining how the function is being used as a method. The
target slot is the class signature for which the method will
be dispatched, and the defined slot the signature for which
the method was originally specified (that is, the one that appeared
in some call to setMethod).
class '>MethodsList for the objects
defining sets of methods associated with a particular generic
function. The individual method definitions stored in these objects
are from class MethodDefinition, or an extension.
Class '>MethodWithNext for an extension used by
callNextMethod.