Read e Write

Usando Read e BufRead, você pode abstrair as fontes de dados do tipo u8:

use std::io::{BufRead, BufReader, Read, Result};

fn count_lines<R: Read>(reader: R) -> usize {
    let buf_reader = BufReader::new(reader);
    buf_reader.lines().count()
}

fn main() -> Result<()> {
    let slice: &[u8] = b"foo\nbar\nbaz\n";
    println!("linhas na _slice_: {}", count_lines(slice));

    let file = std::fs::File::open(std::env::current_exe()?)?;
    println!("linhas no arquivo: {}", count_lines(file));
    Ok(())
}

Da mesma forma, Write permite abstrair a escrita de dados do tipo u8:

use std::io::{Result, Write};

fn log<W: Write>(writer: &mut W, msg: &str) -> Result<()> {
    writer.write_all(msg.as_bytes())?;
    writer.write_all("\n".as_bytes())
}

fn main() -> Result<()> {
    let mut buffer = Vec::new();
    log(&mut buffer, "Olá")?;
    log(&mut buffer, "Mundo")?;
    println!("Registrado: {:?}", buffer);
    Ok(())
}