What is a .NET managed module?

Question

I know it's a Windows PE32, but I also know that the unit of deployment in .NET is an assembly which in turn has a manifest and can be made up of multiple managed modules.

My questions are :

1) How would you create multiple managed modules when building a project such as a class lib or a console app etc.

2) Is there a way to specify this to the compiler(via the project properties for example) to partition your source code files into multiple managed modules. If so what is the benefit of doing so?

3)Can managed modules span assemblies?

4)Are separate file created on disk when the source code is compiled or are these created in memory and directly embedded in an assembly?

EDIT:

@Jon:

For 2):So, does compiling/building source in visual studio always create a single managed module? If so then I fail to understand as to why VS doesn't provide a mechanism to do so in spite of the fact that .NET supports doing so. I agree that it would be unmanageable to create an assembly with modules from different languages. Is that the only reason why .NET allows creating multi module assemblies? I read in Richter's CLR via C# that modules can also span assemblies, and this can help keep assembly sizes down, and reduce memory footprint by downloading assembles on demand when certain functionality is invoked for the first time, but I'm not quite sure as to why would one want to span a module across assemblies, why not just create a new assembly which implicity creates a new module in the process. You would still gain the same benefits.

Item 4) was in regards to ".netmodule" files. As part of the VS build process I haven't seen any ".netmodule" files created in the obj directory. I've typically noticed .pdb, .dll/.exe and a *FileListAbsolute file and hence the question on whether any separate files are created for managed modules.

EDIT: @Jon: Here is the excerpt from CLR via C#(3rd edition) Pg 43: Maybe I'm misreading this but it sounds to me that a module (which is a file belonging to an assembly) can be downloaded on demand.

"For example, an assembly can consist of several types. You could put the frequently used types in one file and the less frequently used types in another file. If your assembly is deployed by downloading it via the Internet, the file with the infrequently used types might not ever have to be downloaded to the client if the client never accesses the types. For example, an independent software vendor (ISV) specializing in UI controls might choose to implement Active Accessibility types in a separate module (to satisfy Microsoft’s Logo requirements). Only users who require the additional accessibility features would require this module to be downloaded.

You configure an application to download assembly files by specifying a codeBase element (discussed in Chapter 3) in the application’s configuration file. The codeBase element identifies a URL pointing to where all of an assembly’s files can be found."

Answer 1

1) You can't do this in Visual Studio. You can do it from the command line using:

csc /target:module Foo.cs Bar.cs

In this case you'd end up with a fle called Foo.netmodule

2) See question 1 - you can't do this from Visual Studio, but you can do it from the command line. I don't know of any benefits. EDIT: I agree with Andrew's statement that you could create an assembly from multiple languages this way - but I believe it would be impractical. You'd have to work out an appropriate dependency chain so that you could build one complete module first, then the next etc... at that point, why not just build separate assemblies in the first place? It would effectively be an extra accessibility domain, admittedly... but that's about all. I believe the disadvantages of this are likely to outweigh the advantages in almost all scenarios. If you really want to build a single assembly, you can always use ilmerge after building separate assemblies.

3) Well, in theory a single module could be included in multiple assemblies, but there'd be no point in doing so - it would create a very confusing system.

4) I'm not really sure what you mean. Visual Studio creates some intermediate files in the obj directory, if that's what you mean. The command line compiler doesn't leave any extra files lying around, but it may create intermediate files which it deletes on completion - I don't really know.

EDIT: I don't believe VS builds modules as an intermediate step. Compiling in Visual Studio always creates a single assembly per project, and that assembly has a single module. When you say that CLR via C# says that "modules can span assemblies" are you sure you don't mean that assemblies can span multiple modules? You can download modules of an assembly on demand, but not the other way round. If you have a specific reference, I could look it up...

Answer 2

You cannot create modules using VS, but you can do it using compiler. Modules are separate files on the file system, it is possible to have several modules in one assembly written in different languages.

EDIT: Also you can put rarely used classes in the separate modules. Such modules will be loaded only when classes are needed.