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  ANSI Common Lisp   7 Objects   7.7 Dictionary of Objects

7.7.34 find-method Standard Generic Function

Syntax:
find-method generic-function method-qualifiers specializers &optional errorp
       method

Method Signatures:
find-method (generic-function standard-generic-function) method-qualifiers specializers &optional errorp

Arguments and Values:
generic-function - a generic function.

method-qualifiers - a list.

specializers - a list.

errorp - a generalized boolean. The default is true.

method - a method object, or nil.

Description:
The generic function find-method takes a generic function and returns the method object that agrees on qualifiers and parameter specializers with the method-qualifiers and specializers arguments of find-method. Method-qualifiers contains the method qualifiers for the method. The order of the method qualifiers is significant. For a definition of agreement in this context, see Section 7.6.3 Agreement on Parameter Specializers and Qualifiers.

The specializers argument contains the parameter specializers for the method. It must correspond in length to the number of required arguments of the generic function, or an error is signaled. This means that to obtain the default method on a given generic-function, a list whose elements are the class t must be given.

If there is no such method and errorp is true, find-method signals an error. If there is no such method and errorp is false, find-method returns nil.

Examples:
 (defmethod some-operation ((a integer) (b float)) (list a b))
 #<STANDARD-METHOD SOME-OPERATION (INTEGER FLOAT) 26723357>
 (find-method #'some-operation '() (mapcar #'find-class '(integer float)))
 #<STANDARD-METHOD SOME-OPERATION (INTEGER FLOAT) 26723357>
 (find-method #'some-operation '() (mapcar #'find-class '(integer integer)))
 Error: No matching method
 (find-method #'some-operation '() (mapcar #'find-class '(integer integer)) nil)
  NIL

Affected By:
add-method, defclass, defgeneric, defmethod

Exceptional Situations:
If the specializers argument does not correspond in length to the number of required arguments of the generic-function, an an error of type error is signaled.

If there is no such method and errorp is true, find-method signals an error of type error.

See Also:
Section 7.6.3 Agreement on Parameter Specializers and Qualifiers

Allegro CL Implementation Details:
None.

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