Macro impl_requester 

macro_rules! impl_requester {
    (
        $name:ident {
            @required{
                $($must_field:ident: $must_type:ty,)+
            };
            @optional{
                $($opt_field:ident: $opt_type:ty,)*
            };
        } -> $fut_ret:ty;
    ) => { ... };
}

A self implemented Type Builder