Outdated information in "unit-type-parameters" chapter?

These posts are really interesting and helpful. But when I try to run the following snippet in [playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=d08e3f51989fb0d6db5283081027c5f1), it seems outdated and reports and error:

> thread 'main' panicked at src/main.rs:18:5:
assertion `left == right` failed
left: 8
right: 0

https://github.com/dtolnay/case-studies/blob/4c3517ad3124fd6c86ae9cfb89dee2d151d78ce5/unit-type-parameters/README.md?plain=1#L328-L348

I checked the implementation of https://github.com/dtolnay/ghost but did not find the difference.