What an interesting perspective on Ruby async, the I/O multiplexing example was quite faschinating to see aswell

Gotta give credit for wonderfully clear writing. You can tell a person understands what they're saying by how well they express it. Reads smooth, and makes me see the author's mental model.

As far as substance: I love ruby libraries that allow you to simply "insert any ruby code". Many libraries tell you to call specific declarative functions, but I think Ruby shines at letting you use Ruby, instead of some limited subset of it. Examples of not-great approaches (imo) are libraries that try to take over how you write code, and give you a special declarative syntax for runtime type checking, building services out of lambdas, composing functions. Ruby's async is an example of "just insert any ruby in here". You can build runtime type checking the same way — allow people to check the value with any ruby code they like. Essentially, I agree with author's sentiment, and wish more people appreciated the beauty of this approach.