le, in <a href="https://doc.rust-lang.org/std/io/"><code>std::io</code></a>, <code>mod mem</code>
provides implementations for
<a href="https://doc.rust-lang.org/std/io/struct.BufReader.html"><code>BufReader</code></a>
and
<a href="https://doc.rust-lang.org/std/io/struct.BufWriter.html"><code>BufWriter</code></a>,
but these are re-exported in <code>io/mod.rs</code> at the top level of the module:</p>

<span class='rusttest'>fn main() {
    // libstd/io/mod.rs

pub use self::mem::{MemReader, BufReader, MemWr