Question

我有一个类消息的实例，我将调用＆＃34; msg＆＃34;。我已经定义了一个班级＆＃34; my-message＆＃34;并希望实例＆＃34; msg＆＃34;现在属于那个班级。

听起来我觉得它应该相对简单，但我不知道该怎么做。改变班级给了我一个我不明白的错误。

(defclass my-message (message)
  ((account-name :accessor account-name :initform nil :initarg :account-name)))

(change-class msg 'my-message :account-name account-name)

ERROR :
While computing the class precedence list of the class named MW::MY-MESSAGE.
The class named MW::MESSAGE is a forward referenced class.
The class named MW::MESSAGE is a direct superclass of the class named MW::MY-MESSAGE.

Answer 1

Sub breaking_count()
    Const Area_x As String = "$D$9:$I$9"
    Const Area_y As String = "$K$9:$P$9"
    Dim Nr As Integer, Count_x As Integer, Col_Ind
    Dim temp_Area As Range

    For Nr = 4 To 1 Step -1
        'With Worksheets(CStr(Nr))
        With Worksheets(Nr)
            If WorksheetFunction.CountIf(.Range(Area_y), "*y*") > 0 Then
                'find the index of "y" in Area_y
                Col_Ind = WorksheetFunction.Match("y", .Range(Area_y))
                'Reset the range Area_y in temp_Area using offset
                Set temp_Area = .Range(.Cells(9, 4).Offset(0, Col_Ind), .Cells(9, 9))
                Count_x = Count_x + WorksheetFunction.CountIf(temp_Area, "*x*")
            Else
                Count_x = Count_x + WorksheetFunction.CountIf(.Range(Area_x), "*x*")
            End If
            MsgBox Worksheets(Nr).Name & " : " & Count_x
            Count_x = 0
        End With

    Next
End Sub

前向引用类是您引用但尚未定义的类。如果查看类的名称，则为The class named MW::MESSAGE is a forward referenced class.。我想你想在另一个包中继承另一个名为MW::MESSAGE的类;您导入的符号可能有问题。

MESSAGE

由于尚未定义The class named MW::MESSAGE is a direct superclass of the class named MW::MY-MESSAGE.类，因此无法创建它的实例。这也是您无法创建任何子类的实例的原因，例如MW::MESSAGE。

Answer 2

这对我有用：

CL-USER>  (defclass message () ())
#<STANDARD-CLASS COMMON-LISP-USER::MESSAGE>

CL-USER> (defparameter *msg* (make-instance 'message))
*MSG*

CL-USER> (describe *msg*)
#<MESSAGE {1002FE43F3}>
  [standard-object]
No slots.


CL-USER> (defclass my-message (message)
           ((account-name :accessor account-name
                          :initform nil
                          :initarg :account-name)))
#<STANDARD-CLASS COMMON-LISP-USER::MY-MESSAGE>

CL-USER> (change-class *msg* 'my-message  :account-name "foo")
#<MY-MESSAGE {1002FE43F3}>

CL-USER> (describe *msg*)
#<MY-MESSAGE {1002FE43F3}>
  [standard-object]

Slots with :INSTANCE allocation:
  ACCOUNT-NAME  = "foo"

请注意，这不是强制转换，因为对象本身会被更改。它现在是另一个类的实例。 cast 通常意味着只是在某些情况下对未更改的内容的解释会发生变化。但这里的实例确实发生了变化，旧的解释不再适用。

如何＆＃34;演员＆＃34;子类的实例？

2 个答案: