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Optional parameters must not be declared on function call.
Example:
Public Function DoAny(Optional ByVal P1 As Long) As Long
If IsMissing(P1) Then
Return 200
EndIf
Return 100
End Function
The call of the function above can be executed without parameter
DoAny()
or can be executed with parameter
DoAny(10)
It can be archieved by the function IsMissing if the parameter will be used by caller.
If mandatory parameters and optional parameters are defined together, the optional parameters must be specified at the end of the function definition.
Public Function DoAny(ByVal P1 As Long, Optional ByVal P2 As Long, Optional ByVal P3 As Long) As Long
Return -1 If IsMissing(P2)
Return -2 If IsMissing(P3)
Return P1 + P2 + P3
End Function
Optional parameters can be given a default value. This eliminates the test for existence with the IsMissing function.
Public Function DoAny(Optional ByVal P1 As Long := 100) As Long
Return P1
End Function
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