struct Foo {
    a: f32,
    b: bool
}

let fields: Fields = ...;
let idents = fields.iter().map(|f| &f.ident);
let members = fields.iter_member();
quote! {
    impl Clone for Foo {
        fn clone(&self) -> Self {
            Self {
                #(#idents: self.#members.clone(),)*
            }
        }
    }
}

impl Clone for Foo {
    fn clone(&self) -> Self {
        Self {
            a: self.a.clone(),
            b: self.b.clone(),
        }
    }
}