Does specifying the OutAttribute on ByRef internal methods currently do anything?

Question

VB.NET doesn't have out parameters, but you can specify <Out()> ByRef on COM and P/Invoke methods to get the same effect for external methods.

Does specifying the same on internal methods (i.e. methods only called by .NET code) actually help the Jitter (or VB.NET compiler)? Or is it currently only useful as a programmer note.

Is it possible it could be used in a future Jitter, or is this attribute lost when compiling?

Mark Hurd · Accepted Answer · 2015-06-03T02:51:27.027

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I've confirmed a VB.NET <Out()> does cause a C# client to require out arguments, so it does seem to be effectively the same.

Also a C# client passes in its arguments with current values into the method, but that's not surprising because, unlike the COM or P/Invoke cases, there's no marshalling to do. (And C# won't allow a property to be set by an out argument directly, so there doesn't seem to be a way to see if C# would optimise away a previous unneeded assignment.)

So it seems the answer is it does help possible future C# clients use the code, and if the jitter ever adjusts the C# equivalent, it would do the same here. Though because languages like VB exist, it can't do much because they don't respect the Out attribute themselves.

edited Jun 03 '15 at 02:51

answered Jul 20 '11 at 10:33

Mark Hurd

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Yes, it is *exactly* the same. The C# `out` keyword compiles down to IL code that contains the `` attribute. VB.NET just doesn't have the keyword. You can verify this for yourself by compiling two test projects and using ILdasm to compare them. – Cody Gray - on strike Aug 11 '12 at 07:17
I'm assuming this refers to the Out attribute in namespace System.Runtime.InteropServices. Is that the case? – jswolf19 Jun 03 '15 at 02:32
@jswolf19 Yes, modified, also in my answers in linked questions. – Mark Hurd Jun 03 '15 at 02:54
@Mark Thanks for the answer ^_^ – jswolf19 Jun 03 '15 at 07:27

Richard Collette · Answer 2 · 2015-01-29T02:10:48.497

I subclassed MembershipProvider with a VB class, we'll call it A, and then subclassed A with a C# class we'll call B. The C# code, B, was not recognizing the fact that the abstract methods in the MembershipProvider had already been implemented in the VB subclass, A, until I applied the OutAttribute in the VB class for parameters that were specified as out in the MembershipProvider base class abstract methods. This has an impact beyond just COM or P/Invoke.

Does specifying the OutAttribute on ByRef internal methods currently do anything?

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