7.7.2 ensure-generic-function [Function]

ensure-generic-function function-name &key argument-precedence-order declare documentation environment generic-function-class lambda-list method-class method-combination
⇒ generic-function

Arguments and Values::

function-name—a function name.

The keyword arguments correspond to the option arguments of defgeneric, except that the :method-class and :generic-function-class arguments can be class objects as well as names.

Method-combination – method combination object.

Environment – the same as the &environment argument to macro expansion functions and is used to distinguish between compile-time and run-time environments.

[Editorial Note by KMP: What about documentation. Missing from this arguments enumeration, and confusing in description below.]

generic-function—a generic function object.

Description::

The function ensure-generic-function is used to define a globally named generic function with no methods or to specify or modify options and declarations that pertain to a globally named generic function as a whole.

If function-name is not fbound in the global environment, a new generic function is created. If

(fdefinition function-name)

is an ordinary function, a macro, or a special operator, an error is signaled.

If function-name is a list, it must be of the form (setf symbol). If function-name specifies a generic function that has a different value for any of the following arguments, the generic function is modified to have the new value: :argument-precedence-order, :declare, :documentation, :method-combination.

If function-name specifies a generic function that has a different value for the :lambda-list argument, and the new value is congruent with the lambda lists of all existing methods or there are no methods, the value is changed; otherwise an error is signaled.

If function-name specifies a generic function that has a different value for the :generic-function-class argument and if the new generic function class is compatible with the old, change-class is called to change the class of the generic function; otherwise an error is signaled.

If function-name specifies a generic function that has a different value for the :method-class argument, the value is changed, but any existing methods are not changed.

Affected By::

Existing function binding of function-name.

Exceptional Situations::

If

(fdefinition function-name)

is an ordinary function, a macro, or a special operator, an error of type error is signaled.

If function-name specifies a generic function that has a different value for the :lambda-list argument, and the new value is not congruent with the lambda list of any existing method, an error of type error is signaled.

If function-name specifies a generic function that has a different value for the :generic-function-class argument and if the new generic function class not is compatible with the old, an error of type error is signaled.

See Also::

defgeneric