I still don't see how you can determine an object's attributes without type information. If you're inside the function, all you know is there's a parameter named item. How can you provide autocomplete there?

All of the examples you gave are from static languages, where the information is known at compile time (except for valgrind, which requires a runtime). The parent to my original post was claiming that you can have the same tooling for Ruby.

Also, you're wrong about Rust. Lifetimes are part of the type system.