I think you’re probably referring to how redefining a struct breaks Revise.jl and you have to restart the REPL? There are some other rough edges but IME this is the most noticeable

You can use Pluto.jl for this kind of rapid prototyping where you might want to change your structs a lot. It works pretty well with Revise, so when you get things the way you like it can move that struct definition out into your package code.

The other common suggestion is to prototype with NamedTuples instead of structs