December 4, 2025
Self calls, comment brawls
What Is "Open Recursion"?
Open recursion explained, and devs kick off a cross‑language cage match
TLDR: A clear explainer shows “open recursion” as methods calling other methods on the same object while honoring overrides. Comments erupted into a language showdown: praise for dynamic dispatch, shade at C’s rigidity, and Go called out for “fake inheritance,” proving this concept decides how your code actually behaves.
A dev accidentally wrote a whole explainer on “open recursion” — the idea that object methods can call other methods on the same object and still respect overrides — using a friendly Dart example. Think: defining all the buttons in one go so they can press each other. The crowd loved the clarity, with glhaynes cheering, “This was really helpful,” while Akronymus sparked a mini-seminar by asking if the example used closures or just names glued to code. Cue a chorus of “explain it like I’m five” and a couple of nerdy fist bumps to Pierce’s TAPL and Essentials of Compilation.
Then the language wars broke out. chubot declared open recursion just feels “natural” in Python/Java/C++/Rust, with C singled out as the strict parent that won’t allow late-night dynamic dispatch. skybrian crashed the party with a spicy Go take: Go’s “struct embedding” looks like inheritance but secretly refuses self-overrides — a bait-and-switch that had Go fans posting “it’s not a bug, it’s a feature” memes. Meanwhile, kazinator went low-level, flexing a garbage collector example where the system hands control back to the object’s own method — nerds calling it the “GC is open for business” moment. Bottom line: the post demystified the term, but the comments turned it into a cross‑language reality show about who really does “self” calls right.
Key Points
- •The term “open recursion” is introduced by Benjamin C. Pierce in Types and Programming Languages.
- •The article models object behavior using a subset of Dart with functions and maps, without classes or methods.
- •Implementing methods that call each other fails in Dart due to lack of function hoisting and declaration ordering issues.
- •Mutually recursive definitions are needed so methods can reference each other simultaneously (e.g., letrec in Scheme/ML).
- •C achieves similar mutual visibility via forward declarations, illustrating cross-language mechanisms for recursion-friendly bindings.