Nightly Rust can speed up your code even more in certain situations. If you don't need compatibility with stable Rust, you might want to check all the nightly features. In some cases, such as kernel development, it's impossible to get all the required functionality using stable Rust. You can use nightly Rust by overriding the default compiler:
rustup override add nightlyOr, you can call cargo with the +nightly flag. These methods will only work if you use rustup to manage your Rust installation, which you probably should if you have the option.
To use nightly features, you will need to use the #![feature] attribute at the crate level. For example, if you want to use the conservative_impl_trait feature, you will need to add #![feature(conservative_impl_trait)] to the beginning of your main.rs or lib.rs files.
Let's see some of the most interesting unstable features. Note that these features will probably change rapidly, and they might have already changed by the time you read this...