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Almost every one of us knows about passing objects by Value and by Reference, it is perhaps one of the lesser cared about aspects in programming. But if left unnoticed, it can cause unexpected results in our applications. This code sample demonstrates how we can pass a value by Reference and by Value in .NET viz. VB.NET and C#.
Save this file as PassVal.vb
Imports System Imports Microsoft.visualbasic Class TestRef Sub Change(ByRef i As String) i = "Changed" End Sub Sub DontChange(ByVal i As String) i = "Some Text" End Sub End Class Class PassValue Shared Sub main() Dim objT As New TestRef() Dim sChange As String = "DotNetExtreme" Dim sDontChange As String = "DotNetExtreme" 'Value of sChange will change MsgBox("Before = " & sChange) objT.Change(sChange) MsgBox("After = " & sChange) 'Value of sDontChange will not change MsgBox("Before = " & sDontChange) objT.DontChange(sDontChange) MsgBox("After = " & sDontChange) End Sub End Class
Compile the file from the command prompt as VBC Passval.vb.
This was first published in October 2003