Ask HN: What features would you add in a computer language?

I was having a discussion with my co-workers about cool features to add in a computer language. I want to know what features would you guys add in a computer language?

I would add:

* traits * PHP's magic functions * coroutine * C/C++ family syntax * Java's OOP * Erlang/Elixir's concurrent model * Elixir's pattern matching * C++'s templates * C++'s operator overload * python's slice * Erlang/Elixir's preemptive green threads * package manager * C#'s property * async/await

What about you guys?