Function doesn't return a value on all codepaths

Question

I got the warning: "Function doesn't return a value on all codepaths" for the following code:

Function Test() As Boolean

    Dim X As Integer = 5

    If X = 10 Then
        Return True
    End If

End Function

I do understand that I won't return a value in all code paths, since the If statement requires X = 10 in order to access Return. But since the default value when creating a function is False, i expect that to be returned when the criteria isn't filled. So the function in reality does return a value on all code paths.

I assume that it is a bad practice to rely on the default value of the function, especially since the function is created to return a value in the first place. Can someone shed a light on the topic and help resolve my confusion?

I can remove the warning by changing the code to:

Function Test() As Boolean

    Dim X As Integer = 5

    If X = 10 Then
        Return True
    Else
        Return False
    End If

End Function

Or

Function Test() As Boolean

    Dim X As Integer = 5

    Return (X = 10)

End Function

why "But since the default value when creating a function is False" the default values are for variables. I think you should go with the second approach then you're good to go and cover all the cases. — Paweł Łukasik
– Paweł Łukasik, Commented Sep 28, 2017 at 9:00

Tim Schmelter · Accepted Answer · 2017-09-28 09:24:52Z

1

since the default value when creating a function is False, i expect that to be returned when the criteria isn't filled

No, that's a wrong expectation. The reason why .NET doesn't do this is obvious: it's a way to prevent you from careless mistakes. Often you simply overlook that your code paths don't return a value, so if the method would assume that you want to return False then it would hide a bug.

So it forces you to provide the return value yourself.

In VB.NET you can also use Exit Function, then you are returning the default value for that type.

MSDN:

If you use Exit Function without assigning a value to name, the procedure returns the default value for the data type that's specified in returntype. If returntype isn't specified, the procedure returns Nothing, which is the default value for Object.

But in my opinion this is bad practice and only there to be downwards compatible with VB6.

There is another way to leave a function without returning anything: if you throw an exception.

So the warning is a way to tell you that you should rethink your logic, it just reminds you that you might have forgotten a case. A final Return something at the end doesn't hurt you anyway:

Function Test() As Boolean
    Dim X As Integer = 5

    If X = 10 Then Return True

    Return False   
End Function

edited Sep 28, 2017 at 9:24

answered Sep 28, 2017 at 9:01

Tim Schmelter

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1 Comment

Elias Wick Over a year ago

Thank you very much for the explanation! I knew I was wrong and needed some guidance! Plus points for providing links and your own code sample! Have a great day Tim!

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