继承

twinBASIC 提供了几种继承机制以支持简单和完整的面向对象编程模式：Implements、Implements Via 和 Inherits。

Implements 的增强

twinBASIC 中的 Implements 有多项增强：

继承的接口

twinBASIC 中的 Implements 允许用于继承的接口——例如，如果你有 Interface IFoo2 Extends IFoo，然后在类中使用 Implements IFoo2，而在 VBx 中这是不允许的。你需要为所有继承的接口（除 IDispatch 和 IUnknown 外）提供方法。类将标记所有接口为可用——你不需要为 IFoo 写单独的语句，它会通过 Set 语句（及其底层的 QueryInterface 调用）自动传递。

多重实现

如果你有一个被多个其他接口继承的接口，你可以编写多个实现，或为所有接口指定一个实现。例如：

IOleWindow_GetWindow() As LongPtr _
    Implements IOleWindow.GetWindow, IShellBrowser.GetWindow, IShellView2.GetWindow

接口中的 'As Any' 参数

Implements 允许用于包含 'As Any' 参数的接口：在 VBx 中，如果你尝试使用任何包含 As Any 参数成员的接口会报错。在 twinBASIC 中，如果你用 As LongPtr 替代 As Any，这是允许的，例如：

Interface IFoo Extends IUnknown
    Sub Bar(ppv As Any)
End Interface

Class MyClass
    Implements IFoo

    Private Sub IFoo_Bar(ppv As LongPtr) Implements IFoo.Bar

    End Sub

Implements Via 实现基本继承

tB 允许类之间的简单继承。例如，如果你有一个实现了 IVehicle（包含方法 Honk）的类 cVehicle，你可以创建子类如 cCar 或 cTruck，继承原始类的方法，这样你可以调用 cCar.Honk 而无需编写单独的实现。

你可以看到 Honk 方法只由父类实现，然后在你点击 CodeLens 按钮从 IDE 中就地运行 Sub 时从子类调用。

Inherits 实现完整 OOP

此选项支持完整的继承和 OOP：派生类可访问（但外部调用者不可）的 Protected 方法和变量、Overridable 和 Overrides 语法、多重继承以及显式基类构造函数。

示例：Animal 类层次

从基类开始：

Private Class Animal
    Protected _name As String
    Protected _dob As Date  ' date of birth

    Public Event Spoke(ByVal sound As String)

    Public Sub New(name As String, dob As Date)
        _name = name
        _dob = dob
    End Sub

    Public Property Get Name() As String
        Name = _name
    End Property

    Public Property Get DOB() As Date
        DOB = _dob
    End Property

    ' Age in whole years based on DOB and today's date
    Public Function AgeYears() As Long
        Dim y As Long
        y = DateDiff("yyyy", _dob, Date)
        If DateSerial(Year(Date), Month(_dob), Day(_dob)) > Date Then y = y - 1
        AgeYears = y
    End Function

    Public Sub Speak()
        Dim s As String
        s = GetSound()
        RaiseEvent Spoke(s)
        Debug.Print _name & " says: " & s
    End Sub

    ' --- Overridable hook for derived classes ---
    Protected Overridable Function GetSound() As String
        GetSound = ""
    End Function
End Class

其他类可以继承：

' ===== Derived: Dog =====
Private Class Dog
    Inherits Animal

    Protected _breed As String

    Public Sub New(name As String, dob As Date, breed As String)
        Animal.New(name, dob)               ' we can explicitly call base constructors from within our constructor
        _breed = breed
    End Sub

    Public Property Get Breed() As String
        Breed = _breed
    End Property

    ' Override:
    Protected Overridable Function GetSound() As String Overrides Animal.GetSound
        GetSound = "woof"
    End Function
End Class

' ===== Further derived: GuardDog (Dog → GuardDog) =====
Private Class GuardDog
    Inherits Dog

    Protected _onDuty As Boolean

    Public Sub New(name As String, dob As Date, breed As String)
        Dog.New(name, dob, breed)           ' we can explicitly call base constructors from within our constructor
        _onDuty = True
    End Sub

    Public Property Get OnDuty() As Boolean
        OnDuty = _onDuty
    End Property
    Public Property Let OnDuty(ByVal v As Boolean)
        _onDuty = v
    End Property

    ' Multi-level override (overriding Dog's override):
    Protected Function GetSound() As String Overrides Dog.GetSound
        If _onDuty Then
            GetSound = "WOOF!"
        Else
            GetSound = "woof"
        End If
    End Function
End Class

这只是摘录，完整的示例 23 中有更多类、用法和关于 twinBASIC 中继承的说明。