Common Lisp：从泛型函数中提取方法

Question

有没有办法从 Common 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，所以如果可以通过 C API - 没关系。
我需要这个来做下一个技巧：

(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

泛型函数 generic-function-methods 在 CLOS 中可用以获取泛型函数的所有方法（参见 CLOS protocol), but note that, for the second part of your question, you can attach a method to a generic function (with add-method) only if the method is detached from any other generic function (see the protocol）：

An error is also signaled if the method is already associated with some other generic function.

您可以通过包 closer-mop 使用这两个函数，独立于任何实现：

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

Common Lisp：从泛型函数中提取方法

Common Lisp: extract methods from generic function

methods

common-lisp

clos

generic-function

mop