Well, you learn something new everyday and today I found out that you can’t have a partial class that spans across projects in C#, i.e. if I have a partial class called MyClass in ProjectA:
I won’t be able to extend it by defining another partial class called MyClass in ProjectB even if I put the new partial class under the same namespace. Now, that’s a bummer.. but when you think about it it actually makes perfect sense!
If partial class across projects were to be allowed, it would represent a huge security risk because it’d allow potentially harmful code to be injected into existing binaries. Imagine if I had a partial class with private methods that I don’t want to expose:
I kept these methods private so others can call them, so then I compile, build and distribute the binaries, and all of a sudden some evil-doer is able to extend my class and do this:
Now that’s no good! OK.. if someone really wants to execute the DoSecretHandshake method, they can always use reflection to do it, but at least it won’t be so easy and indeed tempting for them to try it..
Oh, and one more thing, a partial class is a compile time only piece of syntactic sugar and the whole thing is still compiled into a single type, in a single project. It does however, allow you to separate a huge class file into multiple files and hence making it easier to organise and manage.