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

[FrankLike via Digitalmars-d]

Hello,everyone,
I've writed some projects  in  C#,find the 'partial' key word is 
very userful,which lets the auto codes in another single file,my 
codes are very easy to update.
But  what the same thing in D?
Thank you,every one.