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Editorial Team
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Asked: 2026-05-13T11:16:28+00:00

When in C# we have the out and ref parameter options, in VB there

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When in C# we have the out and ref parameter options, in VB there is a only one: ByRef.

Now, little ‘problem’ when trying to ‘eliminate’ the compiler warning saying that test was not initialized before passing as argument:

Dim test As MyParsableClass ' = Nothing  need imperatively?? '
' some code ... '
MyParsableClass.TryParse("value", test) ' warning on "test" here

the class brief declaration: 

Class MyParsableClass

  Public Shared Function TryParse(ByVal value As String, _
    ByRef myParsableClass As MyParsableClass) As Boolean
    myParsableClass = Nothing
    If True Then
      ' parse code OK'
      myParsableClass = New MyParsableClass()
      Return True
    Else
      ' parse code NOK '
      ' myParsableClass remains Nothing '
      Return False
    End If

  End Function

End Class

maybe a solution was to declare

...Optional ByRef myParsableClass As MyParsableClass = Nothing)

but I can’t set this parameter as optional one. What will happen if I’ll miss it?

PS. (edit)

In the real project, my “parsable” class is MyHour with Hour and Minute properties. I wrote already the Parse(value as String) with a FormatException, but I think the code could be more clear, compact and quick when I will not use try catch blocks…

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1 Answer

  1. Editorial Team

    I do not believe it’s possible to prevent this warning, without an explicit assignment.

    Different languages have different features/facilities – if they didn’t, there’d only be one programming language 🙂 In this case, yes, VB doesn’t pretend that there are two types of ref parameters, as C# does – so far as the CLR is concerned, “out” doesn’t exist.

    And I’m not sure what peSHIr is talking about – TryParse was added to later releases of the BCL for precisely the situation where a parse is as likely to fail as to succeed – so you can take a faulting path without requiring an exception to be thrown.

    Edit

    To add – the reason you don’t get a warning for many of the built in types for which a TryParse exists (e.g. Int32) is because they’re Structs/Value types, and hence always have a value. If your class is simple enough, would it be logical for it to be a Structure instead?

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