通用Lisp:从泛型函数中提取方法

Question

是否有方法从通用Lisp中的泛型函数中提取方法列表？

例如：

(defmethod say ((self string)) ; method-0
  (format t "Got string: ~a~%" self))

(defmethod say ((self integer)) ; method-1
  (format t "Got integer: ~a~%" self))

(defmethod say ((self symbol)) ; method-2
  (format t "Got symbol: ~a~%" self))

(extract-methods-from-generic 'say) ; -> (method-0-obj method-1-obj method-2-obj)

更具体地说，我的目标是ECL，所以如果这可以通过can实现--没关系。

我需要这个来做下一招：

(defgeneric merged-generic ())

(loop for method
      in (extract-methods-from-generic 'some-generic-0)
      do (add-method merged-generic method))
(loop for method
      in (extract-methods-from-generic 'some-generic-1)
      do (add-method merged-generic method))

Answer 1

在CLOS中可以使用泛型函数generic-function-methods来获取泛型函数的所有方法(请参见CLOS协议)，但请注意，对于问题的第二部分，只有当方法与任何其他泛型函数分离(参见协议)时，才能将方法附加到泛型函数(带有add-method)：

如果方法已经与其他泛型函数相关联，则还会发出错误信号。

您可以通过包近亲拖把使用这两个函数，而不依赖于任何实现：

CL-USER> (ql:quickload "closer-mop") 
("closer-mop")
CL-USER> (in-package :closer-mop)
#<Package "CLOSER-MOP">
C2MOP> (defgeneric say (x))
#<COMMON-LISP:STANDARD-GENERIC-FUNCTION SAY #x30200176712F>
C2MOP> (defmethod say ((self string)) ; method-0
  (format t "Got string: ~a~%" self))

(defmethod say ((self integer)) ; method-1
  (format t "Got integer: ~a~%" self))

(defmethod say ((self symbol)) ; method-2
  (format t "Got symbol: ~a~%" self))
#<COMMON-LISP:STANDARD-METHOD SAY (SYMBOL)>
C2MOP> (generic-function-methods #'say)
(#<COMMON-LISP:STANDARD-METHOD SAY (SYMBOL)> #<COMMON-LISP:STANDARD-METHOD SAY (INTEGER)> #<COMMON-LISP:STANDARD-METHOD SAY (STRING)>)
C2MOP> (defgeneric merged-generic (x))
#<COMMON-LISP:STANDARD-GENERIC-FUNCTION MERGED-GENERIC #x30200181B74F>
C2MOP> (add-method #'merged-generic (first **))

#<COMMON-LISP:STANDARD-METHOD SAY (SYMBOL)> is already a method of #<COMMON-LISP:STANDARD-GENERIC-FUNCTION SAY #x30200165863F>.
   [Condition of type SIMPLE-ERROR]
; Evaluation aborted on #<SIMPLE-ERROR #x3020016719FD>.
CL-USER> (let ((first-method (first (generic-function-methods #'say))))
           (remove-method #'say first-method)
           (add-method #'merged-generic first-method))
#<COMMON-LISP:STANDARD-GENERIC-FUNCTION MERGED-GENERIC #x302000DC54DF>
CL-USER> (merged-generic "a string")
Got string: a string
NIL