[Vala] How to implement cast in vala?

[Akira Nakagawa <matyapiro31 gmail com>]

Hi all.
I have an experience with C#, so I could do this in vala, too.
public static implicit Class2 (Class1 val) {
    return val.getClass2();
}
There is no example or reference for vala,
So how can I explicit/implicit-ly  convert class type in vala?