[@zero_alloc] and the compiler refuses to build if anything in its call tree touches the heap." name=description><br>The feature in OxCaml that more languages should steal - The Consensus<br>The Consensus Weekly<br>Get new deep dives, plus jobs and funding in software infrastructure, free in your inbox every week.Subscribeocaml<br>The feature in OxCaml that more languages should steal<br>In most languages, you hunt allocations down with a profiler and they creep back the moment you touch the hot path.
Jane Street's superset of OCaml lets you flip that around: annotate a function with [@zero_alloc] and the compiler refuses to build if anything in its call tree touches the heap.By Phil Eaton·June 27, 2026<br>You are getting early access to this article as a subscriber. Your support makes articles like this possible. Thank you.OxCaml, Jane Street’s superset of OCaml, allows you to assert that entire functions do not allocate (on the heap). And if you start allocating within that call tree, the compiler will fail and tell you that you allocated. While you might be able to achieve this with static analysis, there are no mainstream languages I know of that let you do this in the compiler itself.In every other language (C, C++, Java, Go, C#, Rust, Zig, OCaml, etc.) the process is reversed: you take a profiler to try and find allocations (usually in loops that happen millions of times). Then you go and eliminate or minimize the allocations. But as soon as you edit a line of code in the hot path, you might forget the context and start allocating again, and you’re back to square one with a profiler.At best, in Zig (and maybe more recent Rust) you might be able to minimize regression through convention by not passing an allocator to a function. But convention can be ignored. Why not let the compiler do the work?In this article we'll take a look at how OxCaml's [@zero_alloc] assertion works.Want to keep reading?<br>The Consensus is a bootstrapped company that depends on your support to produce articles like this.Subscribe or sign in for unlimited access.Otherwise, enjoy any of our older articles. And check back on this article in a week!Join the free weekly newsletter and we'll let you know when it's out, along with new jobs and funding in software infrastructure.Join
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ocamloxcamlprogramming languages<br>Enjoyed this article?<br>Get new deep dives like this one, plus new jobs and funding news in software infrastructure, free in your inbox every week.SubscribeWant exclusive articles and to back our work? Become a paid subscriber.Written by<br>Phil Eaton<br>Phil is the founder of The Consensus. Before this, he contributed to Postgres products at EnterpriseDB, cofounded and led marketing at TigerBeetle, and was an engineering manager at Oracle. He runs the Software Internals Discord, the Software Internals Email Book Club, and co-runs NYC Systems. @eatonphil<br>Noticed a mistake? Have a question or comment? Write to the editor.<br>Comments
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