chinese https://github.com/sunface/rust-by-practice/blob/e0e88e963a3d2c96029e1e3dca3397d38db78cab/zh-CN/book.toml#L22 English https://github.com/sunface/rust-by-practice/blob/e0e88e963a3d2c96029e1e3dca3397d38db78cab/en/book.toml#L22 Rust play ground version is already 2021 on English pages. Chinese version should have the same version. And, some solutions don't work under 2018, e.g. [this](https://github.com/sunface/rust-by-practice/issues/500).
chinese
https://github.com/sunface/rust-by-practice/blob/e0e88e963a3d2c96029e1e3dca3397d38db78cab/zh-CN/book.toml#L22
English
https://github.com/sunface/rust-by-practice/blob/e0e88e963a3d2c96029e1e3dca3397d38db78cab/en/book.toml#L22
Rust play ground version is already 2021 on English pages. Chinese version should have the same version.
And, some solutions don't work under 2018, e.g. this.