When a func is called, its body will run with the provided input params. The func will return one or more result values if at least one result type was declared.

You can directly return from RuneCountInString func because it returns an int as well.

func Len(s string) int {

return utf8.RuneCountInString(s)

} lettersLen := Len("Hey!")

This func uses an expression next to a return.