用于类java继承的VBA组合

Question

在这个问题上展开一点VBA继承模式

我正在VBA中复制一个基本的继承模式，但我想了解是否有更有效和简洁的方法来实现这一点。

考虑一下这个小测试用例。

伊尼马尔。cls公司

'declaration
Public Sub eat()
End Sub

Public Sub breathe()
End Sub

nimal.cls：超类

Implements IAnimal

' method implementation
Private Sub IAnimal_eat()
    Debug.Print "I'm eating something..."
End Sub

Private Sub IAnimal_breathe()
    Debug.Print "I'm brething..."
End Sub

Cat.cls：动物的子类

Private super As IAnimal

Implements IAnimal

Private Sub Class_Initialize()
    Set super = New Animal
End Sub


'#------------------------------------------------
' methods called when object is accessed as an IAnimal implementor. 
' I HAVE TO re-implement all of them also here in the subclass (in java I don't need to. It's sufficient to implement them in the superclass)
Private Sub IAnimal_eat()
    Me.eat
End Sub

Private Sub IAnimal_breathe()
    Me.breathe
End Sub


'#--------------------------------------------------
' subclass-only methods
' To access those methods I MUST DECLARE the object as Cat (Dim tom as Cat)
Public Sub meow()
Debug.Print "meow..."
End Sub


'#------------------------------------------------ 
' superclass methods
' Since I need to declare the cat object as a Cat (see above)
' I'm FORCED TO explicitly re-implement all of the superclass methods,
' even those that I don't need to override
' otherwise I can't access them

'@Override
Public Sub eat()
    Debug.print "I'm  eating a fish!"
End Sub

'I'm forced to re-implement also this method, in order to use it directly on a *Cat* object
'@Unnecessary-Override
Public Sub breathe()
    super.breathe 
End Sub

Test.bas

Sub Main()

    Dim snowball As IAnimal
    Set snowball = New Cat

    Dim tom As Cat
    Set tom = New Cat

    snowball.meow  'ERROR Method or data member not found <---- cannot access the Cat-only method "meow"
    tom.meow  '<--- prints "meow"

    ' creates a Dog, another subclass of Animal
    Dim pluto As Dog
    Set pluto = New Dog

    'create a collection for all my animals
    Dim myPets As Collection
    Set myPets = New Collection

    myPets.Add tom
    myPets.Add pluto

    Call feed(myPets) '<---- prints
                            'I 'm eating a fish
                            'meow...
                            'I 'm eating a bone
                            'woof...

End Sub

' a routine for showing how to manage an heterogeneous collection of animals
Sub feed(animals As Collection)

    For Each a In animals

        a.eat

        If TypeOf a Is Cat Then
            a.meow
        End If

        If TypeOf a Is Dog Then
            a.woof
        End If

    Next

End Sub

通过这样做，我可以：

• 对Cat和Dog对象调用eat（）方法，并具有特定的重写行为

这似乎可行，但很麻烦：假设您需要实现许多动物子类（狗、鸟、犰狳、鸭嘴兽、Demogorgon等等）。上述模式迫使您：

1. 在所有子类上重新实现IAnimal接口的所有方法

所以问题是：有没有更有效/简洁的方法来实现这个示例（并限制每个子类的代码重写）？

Answer 1

tom首先不应该声明As Cat；feedhtml" target="_blank">过程是多余的：

Sub Main()    
    Dim tom As IAnimal
    Set tom = New Cat    
    tom.eat    
End Sub

现在，在Cat类中，这些成员不需要存在：

'Superclass methods --- I have to explicitly override all methods :(
Public Sub eat()
    super.eat 
    Debug.print "...a fish!"
End Sub

在SOLID/OOP中，您针对接口而不是具体类型进行编码——这就是为什么tom是I动物而不是Cat。通过它的I动物接口访问，Cat.eat是完全冗余的，并且表明Cat做了I动物不做的事情，这违反了SOLID原则：突然间，I动物是Cat变得相关，它不应该是，因为多态性允许I动物是任何东西，并且Liskov替换原则（LSP-“SOLID”的“L”）说任何与I动物一起工作的代码都应该能够以相同的方式工作，无论它给出了该接口的实现。

遵守这些原则意味着任何I动物实现都不应该在其默认接口上有I动物成员的副本（例如Cat.eat，vsIAnimal.eat），这完全消除了您的观点#2：

至于第一点...

1. 重新实现I动物接口的所有方法

这是编译器的要求，不是VBA的怪癖：无论是在Java、C#还是VBA中，都不能说“我正在实现一个接口”。。。没有实现其成员。当然是Java