Visual Basic .NET Language ByVal and ByRef keywords ByVal keyword
Example
ByVal keyword before method parameter (or no keyword as ByVal is assumed by default) says that parameter will be sent in a way not allowing the method to change (assign a new value) the variable underlying the parameter.
It doesn't prevent the content (or state) of the argument to be changed if it's a class.
Class SomeClass
Public Property Member As Integer
End Class
Module Program
Sub Main()
Dim someInstance As New SomeClass With {.Member = 42}
Foo (someInstance)
' here someInstance is not Nothing (still the same object)
' but someInstance.Member is -42 (internal state can still be changed)
Dim number As Integer = 42
Foo(number)
' here number is still 42
End Sub
Sub Foo(ByVal arg As SomeClass)
arg.Member = -arg.Member ' change argument content
arg = Nothing ' change (re-assign) argument
End Sub
Sub Foo(arg As Integer) ' No ByVal or ByRef keyword, ByVal is assumed
arg = -arg
End Sub
End Module
