Comment by array_key_first

It's not a "hack" because many language DO NOT let you store functions with state. Gleam does, I write PHP, and that does as well.

PHP has interfaces and whatnot, but a lot of the time I do polymorphism by just having a class that has Closure members. When you can arbitrarily pass around functions like that, it's basically equivalent to an interface or abstract class, with a bit more flexibility.