Macro wrap_write_handler 

macro_rules! wrap_write_handler {
    ($ vis : vis struct $ name : ident ; impl WriteHandler { $ ($ (# [$ 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 WriteHandler { $ ($ (# [$ attrs_name : meta]) * fn $ method_name : ident (& $ self : ident $ (, $ arg_name : ident : $ arg_type : ty) * $ (,) ?) $ (-> $ return_type : ty) ? { $ ($ body : tt) * }) * }) => { ... };
}

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

Example

wrap_write_handler! {
    struct MyWriteHandler {
        payload: String,
    }

    impl WriteHandler {
        // ...
    }
}

fn make_my_struct() -> WriteHandler {
    MyWriteHandler::new("payload".to_string())
}