Enumerable's Ugly Cousin, a deep dive into Enumerator

Everyone loves Ruby's Enumerable module. What about Enumerator? Many of us don't what Enumerator is or why it's useful. It's time to change that. We'll (finally?) understand why Enumerator is important and unveil the "magic" of how it works. After learning how to get started with Enumerator, we'll build up to some diverse use cases, including web crawlers and recurring events. We'll jump from crazy ideas, like emulating lazy sequences more common in functional programming languages, to sane takeaways for more common problems. Even if you've been programming Ruby for years, you may see something new or, at least, see a familiar problem with a fresh perspective. Even if you don't adopt Enumerator into your daily work, you'll come away with a deeper understanding of its advantages and how it complements its famous relative.