# \#primitive

**URL:** https://racket.discourse.group/tag/primitive/186.md

[Latest](https://racket.discourse.group/latest.md) · [Categories](https://racket.discourse.group/categories.md) · [Tags](https://racket.discourse.group/tags.md)

---

## [Why is this \`unsafe-set-car!\` so much slower than \`unsafe-set-immutable-car!\`?](https://racket.discourse.group/t/why-is-this-unsafe-set-car-so-much-slower-than-unsafe-set-immutable-car/2282)

<div class="topic-metadata">

**Author:** [@MartianMoorGrove](https://racket.discourse.group/u/MartianMoorGrove)\
**Replies:** 2\
**Last updated:** [September 5, 2023, 7:27pm UTC](https://racket.discourse.group/t/why-is-this-unsafe-set-car-so-much-slower-than-unsafe-set-immutable-car/2282 "2023-09-05T19:27:56Z")

</div>

Here in Racket v8.10 CS I have implemented unsafe-set-car! in a way that is equivalent (I think) to unsafe-set-immutable-car! which is provided by racket/unsafe/ops: #lang racket/base (module prim racket/base (requi…