I've always said that if you don't have some serious gripes with a programming language or framework, then you don't know it well enough yet. Over more than a decade of using them, I've found plenty of issues with both Ruby and Rails. That I keep using them either says something about their merits or my character flaws. (It's the former.)
Service objects, a popular design pattern in the Ruby on Rails community, are analogous to higher-order functions, and we can demonstrate that more clearly by refactoring one into a Proc without changing its API.
Out of the box, phlex-rails currently doesn't support parameterized layouts. I found a quick way to hack support in.
Kevin Newton's explanations of how YARV works alerted me to a couple of edge cases in Ruby that I'd never thought about.