Is it possible to access struct fields from within a trait?

Traits are used to group some functions to be implemented from a struct, but is it possible to access struct fields from within the trait?

I could imagine declaring fields inside the trait so that the fields are abstracted as well. I haven't found such a syntax; is there any other solution? Otherwise, it wouldn't be possible to have non-static methods using a trait, would it?

I know object oriented programming from C# and I'm playing around with Rust, trying to adapt the OOP functionality I already know from C#.

This sounds like you're misunderstanding how traits work. Traits can't have fields. If you want to provide access to a field from a trait, you need to define a method in that trait (like, say, get_blah).

If you're asking whether you can access fields of a struct from within that struct's implementation of a trait, then yes. The struct knows its own type, so there's no problem.

trait Pet {
    fn is_smelly(&self) -> bool;
}

struct Dog {
    washed_recently: bool,
}

impl Pet for Dog {
    fn is_smelly(&self) -> bool {
        !self.washed_recently
    }
}

If you're writing a default implementation of a trait (i.e. defining a method body within the trait), then no, you can't access fields. A default implementation can only use methods that are defined on the trait or in a super trait.