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Function

ensure-generic-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-namea 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-functiona 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

Backlinks

defgeneric, Function Forms, Introduction to Generic Functions, Objects Dictionary, Safe and Unsafe Calls, standard-generic-function, Symbols in the COMMON-LISP Package