That method is marked unstable, which means you can't use it on the stable releases of Rust. The only way to use it is to do both of the following: 1. Use nigh

That method is marked unstable, which means you can't use it on the stable releases of Rust. The only way to use it is to do both of the following: 1. Use nightly Rust. 2. Explicitly enable the `io` feature with a special directive in your source code.