[masklinn]

> > a borrow checker

> What exactly do you mean? How does it differ from any other language's type system?

Part of rust's type system is sub-structural: by default, Rust's types are affine, which means you can only use them once (at most, not exactly).

Now this is not super convenient to use and could have efficiency issues (e.g. any time you want to check a value in a structure you'd have to return the structure so the caller can get it back), so to complement this you can borrow (create a reference). The borrow checker is the bit which checks that borrows satisfy a bunch of safety rules, mostly that a borrow can't outlive its source, and that you can have a single mutable borrow or any number of immutable borrows concurrently.

The borrow checker provides for memory-safe pointers to or into a structure you're not the owner of, with no runtime cost.