'partial' keyword in C# is very good for project , what's the same thing in D?

[Kagamin via Digitalmars-d]

I work on a big C# project with forms and controls designed in 
both ways: some are split into partial classes, some mix 
generated code with user code. Can't remember any issue with it, 
and difference is visible only when you realize, that the code is 
indeed in the same file, which may or may not happen.