How to pretty-print in Rust

Today, I accidentally found out that instead of using {:?} to debug print, if one just adds an extra # like {:#?} the variable is pretty printed.

This makes sense for struct rather than simple data types like numbers or strings.

The interesting part (for me at least) is how I “discovered” it 😄

When I was printing a struct (for debugging 🙈) VS Code (I think rust analyzer plugin) showed a popup how the struct does not implement Display ¹

I usually ignore the popup. But this time words pretty print caught my eyes.

Moral of the story : It pays to (carefully) read the error messages 😄

The exact error is :

= help: the trait `std::fmt::Display` is not implemented for `......`
= note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead

This is mentioned in the Rust book, but the specific got buried in the wall of text. Unlike the popup, which made me pay attention