Macro wrap_view_delegate 

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

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

Example

wrap_view_delegate! {
    struct MyViewDelegate {
        payload: String,
    }

    impl ViewDelegate {
        // ...
    }
}

fn make_my_struct() -> ViewDelegate {
    MyViewDelegate::new("payload".to_string())
}