Does C# 4 optimize away namespaces in a manner that previous C# versions did not?

Question

This question is for interest sake. I'm working with a third-party library and came across the following documentation on a CMS.Security.Dummy class:

DO NOT DELETE THIS CLASS - This class prevents the compiler from dropping entire namespace under .NET 4.0.

Does anybody know, or can anybody speculate why .NET 4 would drop the namespace if the dummy class were removed?

Because .NET 4 is explicitly named in the source code comment, I assume previous C# versions exhibit behaviour that do not require this dummy class. That's purely speculative though.

Screen shot

Decompiled Source Code

#region Assembly CMS.SettingsProvider.dll, v4.0.30319 // ...\solution\wwwroot\Bin\CMS.SettingsProvider.dll #endregion  using System;  namespace CMS.Security {     // Summary:     //     DO NOT DELETE THIS CLASS - This class prevents the compiler from dropping     //     entire namespace under .NET 4.0.     public class Dummy     {         // Summary:         //     DO NOT DELETE THIS CLASS - This class prevents the compiler from dropping         //     entire namespace under .NET 4.0.         public Dummy();     } } 

Answer 1

A little-appreciated fact is that there is no such thing as a "namespace" from the point of view of the underlying CLR type system. Rather, it's just a convention that we say that a type that contains periods in its name is "a member of a namespace". Logically there is no difference at all between the legal code:

namespace N {     class C  {} } 

and the psuedo-code:

class N.C {} 

C# forces you to pretend this pleasant fiction is reality, but it is just a fiction -- from the perspective of the CLR type system, of course. From the perspective of the C# compiler, of course namespaces are "real". They just don't correspond to anything in metadata other than a portion of the name of a type.

In short: if you make an assembly with an "empty" namespace then the "namespace" doesn't exist at all in the compiled binary. A "namespace" only comes into existence when there is a type in the library that has periods in its name.

Now, why you would care about ensuring that an "empty" namespace has some presence in the binary form, I have no idea.

I assume previous C# versions exhibit behaviour that do not require this dummy class

Nope. Every version of C# since 1.0 throws away empty namespaces.

Answer 2

Given that the namespace doesn't contain any members (without that class), I'm not sure there's even the concept of a namespace at that point... nor would I expect it to be useful anyway.

I've just tried to reproduce this with the C# 2 compiler, and I can't see any trace of an empty namespace within the IL.