the code from P.520: ```rust $( fields.insert($crate::ToString::to_string($key), json!($value)); )* ``` the code in this repository is: ```rust $( fields.insert($crate::macros::ToString::to_string($key), json!($value)); )* ``` It should use the second version `$crate::macros::ToString` because `ToString` is private, just like `HashMap`? :smile: