Is there a VB.NET equivalent of C# out parameters?

Question

Does VB.NET have a direct equivalent to C# out function parameters, where the variable passed into a function does not need to be initialised?

Answer 1

No, there is no equivalent of the out keyword in VB.

However, VB does automatically initialise all local variables in a method, so you can use ByRef without needing to explicitly initialise the variable first.

Example:

Sub Main()   Dim y As Integer   Test(y) End Sub  Sub Test(ByRef x As Integer)   x = 42 End Sub 

(If you examine code in the framework (for example Double.TryParse), you may see the <OutAttribute> added to parameters, but that only makes a difference when the call is marshalled for COM interop or platform invoke.)

Answer 2

No, there is no equivalent construct that allows a non-initialised variable to be passed to a method without a warning, but, as mentioned in my question and answer specifying an <Out()> attribute on a ByRef parameter definition, although VB ignores it, is treated by C# as an out parameter.

So, I would pre-initialise reference variables to Nothing and specify <Out()> ByRef to signify the intention (that will work if C# users ever access your methods).

If you feel you know when you intend to access the default Nothing in otherwise unassigned reference variables you can set the "Warning configuration" "Use of variable prior to assignment" to "None" at the Project level (Project Properties > Compile, and you probably want to set Configuration to "All Configurations" before changing this setting), or, in VS2015 (VB.NET 14), you can use #Disable Warning BC42030.