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.
Of course dynamic dispatch can be implemented in almost every language. The Linux kernel uses dynamic dispatch with C!
But that's a hack, not a language feature.