[stouset]

And I had yet to find a single practical application for closures, right up until the moment I started using Ruby (and later, Rust).

Turns out that they’re so useful in practice that they’ve been bolted on to—as far as I can tell—nearly every language in widespread use today. None of these languages “needed” such an improvement. Billions of lines of Java and C# were written without this feature. And yet today it would be virtually unthinkable to release a language without them.

[dimgl]

I feel like closures are a consequence of having functions as first class citizens, so it's not exactly a direct comparison. But I guess I see your point.