Macro encode_map 

macro_rules! encode_map {
    (
        $field_number:expr,
        $var:expr,
        $key_access:path,
        $value_access:path,
        $key_wire_type:expr,
        $value_wire_type:expr,
        $encoder:expr,
        $key_encode_fn:path,
        $value_encode_fn:path,
    ) => { ... };
}