Why an optional argument returns "Missing" in a user defined function (UDF) instead of empty?

[makiwara]

Question1: The default value of a variant is empty, so why not empty in a UDF, if I don't define it?
Question2: So I test every datatype by its default value to see if it has been given or not, except variant, where I use IsMissing instead of empty. Is this correct?

Thank you very much! Have a nice day!

 

[6StringJazzer]

Please show the code for your UDF.

 

[RoryA]

There is a difference between supplying an empty variant, and not supplying anything.

 

[makiwara]

Function Sum2 (optional Number as variant) as variant

If IsEmpty(Number) then
msgbox "empty"
end if

End function

This throws error, I have to test it with IsMissing(Number), empty does not work. Optional variant status is missing right at the beginning of the function.

 

[Jaafar Tribak]

It seems that when passing an optional variant argument , the argument is given a default value pointing to some error value "Error" meaning that the optional variant argument is actually not Empty that's why IsEmpty(Argument) returns False.

Sub Func(Optional ByVal arg As Variant)
    MsgBox TypeName(arg)  '<== returns Error
End Sub

Sub Test()
    Call Func
End Sub

It seems from the above that IsError can be used as an alternative to IsMissing

Sub Func(Optional ByVal arg As Variant)
    If IsError(arg) Then
        MsgBox "IsError - argument not passed"
    End If
    If IsMissing(arg) Then
        MsgBox " IsMissing - argument not passed"
    End If
End Sub

Sub Test()
    Call Func
End Sub

Why an optional variant argument is given the Error default value while a non initialized variant variable is given the Empty value , I don't know.

 

[RoryA]

But that would also be triggered by you passing an error value, rather than not passing a value at all. I think that the value Missing is a specific error value, and should therefore be tested for using IsMissing.

 

[makiwara]

It seems that when passing an optional variant argument , the argument is given a default value pointing to some error value "Error" meaning that the optional variant argument is actually not Empty that's why IsEmpty(Argument) returns False.

Sub Func(Optional ByVal arg As Variant)
    MsgBox TypeName(arg)  '<== returns Error
End Sub

Sub Test()
    Call Func
End Sub

It seems from the above that IsError can be used as an alternative to IsMissing

Sub Func(Optional ByVal arg As Variant)
    If IsError(arg) Then
        MsgBox "IsError - argument not passed"
    End If
    If IsMissing(arg) Then
        MsgBox " IsMissing - argument not passed"
    End If
End Sub

Sub Test()
    Call Func
End Sub

Why an optional variant argument is given the Error default value while a non initialized variant variable is given the Empty value , I don't know.

Thank you very much for both of you, for the explanation.