英文:
How to implement `cl-print-object`?
问题
我正在使用''eieio' 和''cl-lib'，并尝试按照此处描述的方法为我的类定义'object-print'方法：
https://www.gnu.org/software/emacs/manual/html_mono/eieio.html#Basic-Methods
"返回一个包含数据对象摘要的字符串作为名称的一部分。"
(apply #'cl-call-next-method this
(format " 值: %s" (render this))
strings))
我想这样做是为了在使用 edebug 时看到对象实例的内容。
当我在自己的代码中实现这个示例时，它会产生错误消息“函数‘render’未被定义”。
除了错误消息之外，Flycheck建议：“‘object-print’是过时的泛型函数（自26.1起）；改用‘cl-print-object’。”我在谷歌上找不到关于‘cl-print-object’函数的任何文档，并且我无法猜出如何实现它：
"返回一个包含数据对象摘要的字符串作为名称的一部分。"
(apply #'cl-call-next-method this
(format " 值: %s" (slot-value this 'value))
strings))
我不知道要提供什么来代替‘(slot-value this 'value)’。它似乎不想要一个槽。
我如何实现‘cl-print-object’函数？或者在 edebug 内部进行调试时，有没有更好的方法来查看 EIEIO 对象实例的内容？
英文:
I am using 'eieio and 'cl-lib and I'm trying to define the object-print method for my class as described here:
https://www.gnu.org/software/emacs/manual/html_mono/eieio.html#Basic-Methods
(cl-defmethod object-print ((this data-object) &optional strings)
"Return a string with a summary of the data object as part of the name."
(apply #'cl-call-next-method this
(format " value: %s" (render this))
strings))
I want to do this so I can see the contents of my object instances when I'm using edebug.
When I implement this example in my own code it produces the error message the function ‘render’ is not known to be defined.
In addition to the error message, Flycheck suggests: ‘object-print’ is an obsolete generic function (as of 26.1); use ‘cl-print-object’ instead. I cannot find any documentation on the cl-print-object function when I Google, and I am failing at guessing how to implement it:
(cl-defmethod cl-print-object ((this card) &optional strings)
"Return a string with a summary of the data object as part of the name."
(apply #'cl-call-next-method this
(format " value: %s" (slot-value this 'value))
strings))
I do not know what to provide instead of (slot-value this 'value). It does not seem to want a slot.
How can I implement the cl-print-object function? Or is there a better way to see the contents of an EIEIO object instance when debugging inside edebug?
答案1
得分: 2
我不理解elisp的CLOSoid系统，但类似这样的东西至少是一个开始：
(defclass foo ()
((x :initform 1
:inirarg :x
:reader foo-x)))
(defmethod cl-print-object ((f foo) stream)
(princ (format "#<%s x %s>"
(class-name (class-of f))
(foo-x f))
stream))
现在：
ELISP> (make-instance 'foo :x 2)
#<foo x 2>
ELISP> (defclass bar (foo) ())
bar
ELISP> (make-instance 'bar :x 2)
#<bar x 2>
显然在实际应用中，你希望从对象中提取更多信息：我不知道是否有CL的print-unreadable-object的等价物，它提供了一种不需要手动处理所有工作的好方法。
英文:
I don't understand elisp's CLOSoid system, but something like this is at least a start:
(defclass foo ()
((x :initform 1
:inirarg :x
:reader foo-x)))
(defmethod cl-print-object ((f foo) stream)
(princ (format "#<%s x %s>"
(class-name (class-of f))
(foo-x f))
stream))
Now:
ELISP> (make-instance 'foo :x 2)
#<foo x 2>
ELISP> (defclass bar (foo) ())
bar
ELISP> (make-instance 'bar :x 2)
#<bar x 2>
Obviously in real life you want to extract more information from the object: I don't know if there is an equivalent of CL's print-unreadable-object which provides a nice approach to this without requiring you do to all the work by hand.
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