问VBA中操作符重载的解决方法

EN

Public Function Add(ByVal other As INumeric) As INumeric
End Function

Public Function Multiply(ByVal other As INumeric) As INumeric
End Function

Public Function Negative() As INumeric
End Function

'[...] etc

Option Explicit
'@PredeclaredID

Public Function Add(ByVal first As Variant, ByVal second As Variant) As Variant
    
    If TypeOf first Is INumeric Then
        On Error GoTo defaultAdd
            Dim numericFirst As INumeric
            Set numericFirst = first
            Set Add = numericFirst.Add(second)

    ElseIf TypeOf second Is INumeric Then
        On Error GoTo defaultAdd
            Dim numericSecond As INumeric
            Set numericSecond = second
            Set Add = numericSecond.Add(first)

    Else
defaultAdd:
        On Error GoTo -1
        On Error GoTo errHandle
            Add = first + second
    End If
    Exit Function
    
errHandle:
    err.Description = "Arguments couldn't be added :( try implementing INumeric"
    err.Raise 5
End Function

Public Function Negate(ByVal value As Variant) As Variant
    'Similar sort of stuff
End Function

'[...] etc

Dim result As Variant
Set result = Maths.Add(INumeric1, INumeric2) 'returns INumeric probably
result = Maths.Add(IsNumeric1, IsNumeric2) 'returns IsNumeric probably

Option Explicit
'@PredeclaredID

Implements INumeric

Public value As Double
Private uncertainty As Double

Public Function Take(ByVal apparentValue As Double, Optional ByVal absErr As Double = 0, Optional ByVal relErr As Double = 0) As Measurement
    With New Measurement
        .value = apparentValue
        If absErr <> 0 Then
            .absoluteErr = absErr
        ElseIf relErr <> 0 Then
            .relativeErr = relErr
        Else
            'must be a perfect number, no errors
            .absoluteErr = 0 'default value so no point
        End If
        Set Take = .Self
    End With
End Function

Public Property Get relativeErr() As Double
    relativeErr = Abs(uncertainty / value)
End Property

Public Property Let relativeErr(ByVal relErr As Double)
    uncertainty = relErr * value
End Property

Public Property Get absoluteErr() As Double
    absoluteErr = Abs(uncertainty)
End Property

Public Property Let absoluteErr(ByVal absErr As Double)
    uncertainty = absErr
End Property

Public Property Get Self() As Measurement
    Set Self = Me
End Property

Public Function toString(Optional ByVal formatWithRelErr As Boolean = True) As String
    If formatWithRelErr Then
        toString = value & "±" & Me.relativeErr * 100 & "%"
    Else
        toString = value & "±" & Me.absoluteErr
    End If
End Function

Private Function INumeric_Add(ByVal other As Variant) As INumeric
    If TypeOf other Is Measurement Then
        Set INumeric_Add = Measurement.Take(Me.value + other.value, absErr:=Me.absoluteErr + other.absoluteErr)
    Else
        Set INumeric_Add = Maths.Add(Me, Measurement.Take(other))
        'or Set INumeric_Add = Measurement.Take(Me.value + other, absErr:=Me.absoluteErr)
    End If
End Function

Private Function INumeric_Multiply(ByVal other As Variant) As INumeric
    If TypeOf other Is Measurement Then
        Set INumeric_Multiply = Measurement.Take(Me.value * other.value, relErr:=Me.relativeErr + other.relativeErr)
    Else
        Set INumeric_Multiply = Maths.Multiply(Me, Measurement.Take(other))
    End If
End Function

Private Function INumeric_Negative() As INumeric
    Set INumeric_Negative = Measurement.Take(-Me.value, absErr:=Me.absoluteErr)
End Function

Sub test()
    Dim a As Measurement, b As Measurement, c As Integer
    Set a = Measurement.Take(10, absErr:=1)
    Set b = Measurement.Take(15, relErr:=0.2)
    c = 3 'treated equiv to Measurement.Take(3, relErr = 0)
    
    Debug.Print "a = "; a.toString; " = "; a.toString(False)
    Debug.Print "b = "; b.toString; " = "; b.toString(False)
    Debug.Print "c ="; c

    Dim aPlusB As Measurement
    Set aPlusB = Maths.Add(a, b)
    Debug.Print "a + b = "; aPlusB.toString
    
    Dim bPlusC As Measurement
    Set bPlusC = Maths.Add(c, b)
    Debug.Print "b + c = "; bPlusC.toString(formatWithRelErr:=False)

    Debug.Print "3.2 + 7.3 ="; Maths.Add(3.2, 7.3)
    
    On Error Resume Next
        Debug.Print Maths.Add("k", 4)
        If err.Number <> 0 Then Debug.Print "Err:"; err.Number; "- "; err.Description
End Sub

a = 10±10% = 10±1
b = 15±20% = 15±3
c = 3
a + b = 25±16%
b + c = 18±3
3.2 + 7.3 = 10.5 
Err: 5 - Arguments couldn't be added :( try implementing INumeric