VBでArrayIndexを検査するSetter/Getter

Option Explicit

Private Function MySize(ByRef a As Variant) As Long
    MySize = UBound(a)
End Function

Private Function MyGet(ByRef a As Variant, ByVal i As Long)
    If LBound(a) <= i And i <= UBound(a) - 1 Then
        MyGet = a(i)
    Else
        Call Err.Raise(50000)
    End If
End Function

Private Sub MySet(ByRef a As Variant, ByVal i As Long, ByVal v As Variant)
    If LBound(a) <= i And i <= UBound(a) - 1 Then
        a(i) = v
    Else
        Call Err.Raise(50000)
    End If
End Sub

Private Sub Command1_Click()
    Dim a() As String
    Dim i As Long
    Dim t As Long
    
    ReDim a(10)
    For i = 0 To MySize(a) - 1
        Call MySet(a, i, i + 100)
    Next
    For i = 0 To MySize(a) - 1
        t = MyGet(a, i)
        Debug.Print "a(" & i & ") = " & a(i)
    Next
End Sub

でどうだ？