Macro wrap_set_cookie_callback 

macro_rules! wrap_set_cookie_callback {
    ($ vis : vis struct $ name : ident ; impl SetCookieCallback { $ ($ (# [$ attrs_name : meta]) * fn $ method_name : ident (& $ self : ident $ (, $ arg_name : ident : $ arg_type : ty) * $ (,) ?) $ (-> $ return_type : ty) ? { $ ($ body : tt) * }) * }) => { ... };
    ($ vis : vis struct $ name : ident $ (< $ ($ generic_type : ident : $ first_generic_type_bound : tt $ (+ $ generic_type_bound : tt) *) , + $ (,) ? >) ? { $ ($ field_vis : vis $ field_name : ident : $ field_type : ty) , * $ (,) ? } impl SetCookieCallback { $ ($ (# [$ attrs_name : meta]) * fn $ method_name : ident (& $ self : ident $ (, $ arg_name : ident : $ arg_type : ty) * $ (,) ?) $ (-> $ return_type : ty) ? { $ ($ body : tt) * }) * }) => { ... };
}

Implement the WrapSetCookieCallback trait for the specified struct. You can declare more members for your struct, and in the impl SetCookieCallback block you can override default methods implemented by the ImplSetCookieCallback trait.

Example

wrap_set_cookie_callback! {
    struct MySetCookieCallback {
        payload: String,
    }

    impl SetCookieCallback {
        // ...
    }
}

fn make_my_struct() -> SetCookieCallback {
    MySetCookieCallback::new("payload".to_string())
}