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Intro to Fireweaver

March 28, 2012 mgroves 0 Comments
Tags: FireWeaver Cecil

I've been trying on and off to figure out Mono.Cecil, and so far it's not very encouraging. It's a bit above my pay grade, it seems.

But all is not lost: I came across a tool while browsing NuGet called FireWeaver. It sits on top of Mono.Cecil, which means it does its work after compilation. It provides you with a way to replace a class with an entire other class. So it's not exactly intercepting or proxying classes, the way other AOP frameworks do: it flat out replaces it and is "essentially duct typing(sic) the entire object definition". I don't know if that's supposed to be "duct taping" or "duck typing", but I rather like the term "duct typing".

Here's a quick example of how it works, taken from the FireWeaver CodePlex site. First, I added FireWeaver with NuGet. Then I created a console app like this:

Compile and run as normal and here's the output:

Before FireWeaver

Next, run the FireWeaver.Bootstrapper.exe tool against your assembly/assemblies. In my case, my Replace class is in the same assembly as the class it's replacing, so my arguments are identical, but you could certainly specify another assembly as the second argument:

And here's the output of the console app after I ran FireWeaver.

After FireWeaver

And here's what the assemblies look like (decompiled) before and after FireWeaver. Warning, your head may explode:

JustDecompile before and after

I'm just as confused about Cecil looking at these JustDecompile screenshots as I was before. But I assure you, it does work.

There's definitely some potential here, since this is a pretty easy tool to use, and integrating FireWeaver into your build script(s) shouldn't be too difficult if you don't want to hit the command line after every build. And it almost looks like pure duck typing brought to C#.

But this could also lead to some really wild code if you aren't careful with it. "Dogs and cats living together, mass hysteria" code.


Matthew D. Groves

About the Author

Matthew D. Groves lives in Central Ohio. He works remotely, loves to code, and is a Microsoft MVP.

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