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Copy-and-Patch: A Copy-and-Patch Tutorial

Copy-and-Patch: A Copy-and-Patch Tutorial

5 comments

·October 14, 2025
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re

Related:

Copy-and-Patch: Fast compilation for high-level languages and bytecode (2020) https://news.ycombinator.com/item?id=40553448 - June 2024 (51 comments)

A copy-and-patch JIT compiler for CPython - https://news.ycombinator.com/item?id=38769874 - Dec 2023 (68 comments)

Copy-and-Patch: Fast JIT Compilation for SQL, WebAssembly, and Others - https://news.ycombinator.com/item?id=28547057 - Sept 2021 (7 comments)

shoo

the accompanying post "How It Works" is worth reading alongside this tutorial

https://transactional.blog/copy-and-patch/

(key terms: abus[e|ing]: 4, force: 3, trick: 1, chance: 1)

weinzierl

I think this technique also lies at the heart of the Cranelift project.

https://cranelift.dev/

aw1621107

IIRC Cranelift doesn't use copy-and-patch. It uses e-graphs [0] as part of its optimization pipeline, though.

Closest thing in (relatively) recent news that uses copy-and-patch I can think of is CPython's new JIT.

[0]: https://github.com/bytecodealliance/rfcs/pull/27

weinzierl

My understanding is that e-graphs take care of selecting the best patch (by examining many options in parallel) but fundamentally it is still copy-and-patch.