I remember finally getting what closures and reduce are when I learned Ruby in 2008 for my first Rails job.

A pivotal moment on the same level as when I finally understood how recursion and pointers work in 1995 in my first semester CS classes (taught in Modula 2), two concepts I had only ever read about in programming books, but not been able to understand on my own.

In 2024 I did Advent of Code in Swift, without using mutable state, custom data types or loops, and used reduce rahther generously. [1]

[1] https://github.com/search?q=repo%3Aantfarm%2FAdventOfCode202...