alot of people use kotlin instead of java regardless of its true powers. one of the main aspects of kotlin is its ability to write high quality functional code.
pure and impure, Nothing and Unit, Inline
lazy and lambda, memoization, stream, eager and lazy evaluation, inifinty with lazy, normal order and applicative order
immutablilty in collections, constance, reusablilty and safety, cost of immutablilty, critical section
creating list and builder for list,