Question

我有名为ParentClass的MustInherit类。我需要能够在不同的地方写下以下内容：

Function TheThing(Of T As ParentClass)(s As String) As ParentClass
    Return New T(s)
End Function

我会写

MustInherit Class ParentClass
    MustOverride Sub New(s As String)
End Class
Class Class_Daughter1
    Inherits ParentClass
    Overrides Sub New(s As String)
        'do whatever
    End Sub
End Class

事实上：

如果我没有声明MustOverride sub new（s as string），那么函数TheThing不知道从ParentClass派生的任何类确实有一个sub new（s as string）
如果我添加它，那么它说新的不能是mustoverride

有没有办法做到这一点？我尝试使用一个Implements，但它没有成功......

PS：如果我只是使用

Function TheThing(Of T As ParentClass)(s As String) As ParentClass
    dim a as new T()
    Return a
End Function

新行不起作用

PS2：这也是不允许的：

Function TheThing(Of T As {ParentClass, iCreatable})(s As String) As ParentClass
    Return New T(s)
End Function
Interface iCreatable
    Sub New() '===> not allowed in interface
End Interface

Answer 1

类的构造函数不能是MustInherit，但如果你想做一些基本相同的东西，你可以这样做：

MustInherit Class ParentClass
    Protected Sub New(s As String)
        Initialize(s)
    End Sub

    Protected MustOverride Sub Initialize()

End Class

您的Daughter类的构造函数必须调用MyBase.New(s)。这样子类需要实现初始化，因为子类需要调用基类构造函数，所以保证将调用Initialize。

Answer 2

我刚刚得到答案（来自朋友）：

Function TheThing(Of T As {New, ParentClass})(s As String) As ParentClass
    Dim res As New T()
    res.Init(s)
    Return res
End Function

MustInherit Class ParentClass
    MustOverride Sub Init(s As String)
End Class

Class Class_Daughter1
    Inherits ParentClass
    Overrides Sub Init(s As String)
        'do whatever
    End Sub
End Class

我唯一无法解决的问题是：我不能写下面的内容（如果编译的话，它将是相同的，但在编译时会相同）：

Function TheThing(Of T As {New(s as string), ParentClass})(s As String) As ParentClass
    return New T(s)
End Function

MustInherit Class ParentClass
    'nothing here
End Class

Class Class_Daughter1
    Inherits ParentClass
    public Sub New(s As String)
        'do whatever
    End Sub
End Class

Public MustOverride sub new（Param as type）

2 个答案: