He meant that the intent (kind) can be factored into the type system too. Instead of using type string for both “unsafe string” kind and “safe string” kind, you

He meant that the intent (kind) can be factored into the type system too. Instead of using type string for both “unsafe string” kind and “safe string” kind, you’d use two different types. So the type system aka compiler can catch a mistake, in addition to your eyes. For example, see https://talks.golang.org/2012/goforc.slide#43 https://talks.golang.org/2012/goforc.slide#43.