Hi Simon,
Please note that the context of your example is not quite the same as the one that I originally responded to. Calling the Dispose method and thus invoking an object's clean up is not the same as making an object unreachable. Many developers believe that setting an "object = nothing" is the same as calling its Dispose method. In fact, the example code posted to which I responded demonstrated that objects are "disposed of in this location" by setting them equal to nothing! A proper example would have called their Dispose method instead. Note too that developers often believe that they need to implement the IDisposable code pattern whenever any unmanaged object is used by a class. This is only true if the unmanaged object is defined with class member scope. Local unmanaged resources should have their Dispose method called in the "Finally" block of a properly formatted try/catch/finally. Many developers are also under the mistaken impression that setting an object to Nothing will destroy it or somehow promote a faster clean up by the garbage collector -- or feel that it is necessary or somehow desirable because that the way it was done in VB6. Often former VB6 developers place extraneous "set object = nothing" statements near the end of every single routine as if they were laying non-effective sacrifices to the ancient VB6 god. All this effort buys them nothing because it does not make the object's clean-up code to execute in a deterministic fashion and it seldom has any impact on the performance of garbage collection. In placing these "set Nothing" statements at the end of their routines developers only succeed in delaying the garbage collector from performing its natural function because the object now becomes reachable until the "set object = nothing" statement has been reached and is executed. To truly understand and appreciate this fully one must know that an object can be garbage collected even before completion of the routine that the object was created in has finished executing. (BTW: Debug compilations extend the life of objects for debugging purposes -- so it is hard to witness the phenomenon that I am describing with the debugger attached; however this is the behavior or "Release" compiled assemblies with no debugger attached). --Paul Mehner -----Original Message----- From: Unmoderated discussion of advanced .NET topics. [mailto:[EMAIL PROTECTED] On Behalf Of Hewitt, Simon C. (Contractor) Sent: Tuesday, January 25, 2005 10:29 PM To: [email protected] Subject: Re: [ADVANCED-DOTNET] Disposing of objects Whilst I agree with most that has been said, I'm not sure the bit about the "setting an object to Nothing does nothing useful for you" is correct in all circumstances - consider the following:- If an object is disposed, it doesn't necessary follow that there are no references to it (e.g. If it was in a collection), therefore any references the disposed object holds exclusively are still reachable. By setting these internal references to nothing/null on disposal (but only when Disposing=true), those owned objects are now candidates for garbage collection. Also, I'm sure I've seen in the framework examples of where an object is disposed, it automatically removes itself from its parent's collection. (Or the other way where a collection is disposed and it sets all of its members' Parent property to null and disposed them - I think this was Control.ControlCollection). Isn't this a fair example of using the dispose pattern for something that doesn't involve unmanaged resources? Cheers Simonx -----Original Message----- From: Unmoderated discussion of advanced .NET topics. [mailto:[EMAIL PROTECTED] On Behalf Of Paul Mehner Sent: 25 January 2005 18:28 To: [email protected] Subject: Re: [ADVANCED-DOTNET] Disposing of objects This IDisposable code pattern should not be placed in all classes. There is only one "best practice". Placing this pattern on all classes would be an "ignorant practice". Not is the code pattern not needed for managed classes, it is not desired either because you are forcing the Garbage Collector to do things it doesn't need to do and making it less efficient at performing its work than it would be if you just left it alone. The code pattern provides a means for allowing classes that need to deterministically perform clean up to accomplish that objective. The Garbage Collector knows what to do (exceedingly well) for all managed resources. Read the Garbage Collection chapter in Jeffrey Ricther's book on Programming the .NET Framework to gain true IDisposable enlightenment. BTW: Setting an object to Nothing does nothing useful for you. In your code sample below you have <object_name> = Nothing. Try: <object_name>.Dispose (or .Close) instead. If an object doesn't have a .Close or .Dispose method you are almost certainly barking up the wrong tree trying to dispose of it with the IDisposable code pattern. --Paul Mehner -----Original Message----- From: Unmoderated discussion of advanced .NET topics. [mailto:[EMAIL PROTECTED] On Behalf Of Knowlton, Gerald F. Sent: Tuesday, January 25, 2005 9:37 AM To: [email protected] Subject: [ADVANCED-DOTNET] Disposing of objects Greetings: We are having somewhat of a lengthy discussion going on here regarding the disposing of objects. One camp wants to put the following code into all classes: Private Disposed as Boolean . . . Public sub Dispose() Implements IDisposable.Dispose Dispose(True) GC.Suppressfinalize(me) End sub Protected Sub Dispose(ByVal Disposing as Boolean) If Disposed then Exit Sub If Disposing then DisposeOfObjects End Sub Private Sub Dispose of Objects <object_name> = nothing End Sub While the other camp says it is not needed unless the class has unmanaged resources. Our question is; which would be the better practice? Best regards, Jerry ================================================================== All BWXT, Inc. Email communications are subject to auditing for adherence to company policy pertaining to waste, fraud and abuse. 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