Code shared from the Rust Playground

playground.rs

use std::io::{self,BufRead,BufReader};

enum Utf8DecoderError<'a> {
    InvalidBytes(&'a [u8]),
    Io(io::Error),
}

struct Utf8Decoder<B: BufRead> {
    reader : B,
    bytes_read: usize
}

enum DecodeResult<'a> {
    EOF,
    Error(Utf8DecoderError<'a>),
    Char(char)
}

impl<B: BufRead> Utf8Decoder<B> {
    fn new(r : B) -> Self {
        Self { reader: r, bytes_read: 0 }
    }
    
    fn decode(&mut self) -> DecodeResult {
        DecodeResult::Char('\0')
    }
}

fn main() {
    let s = String::from("Hello, world!");
    let b = BufReader::new(s.as_bytes());
    let decoder = Utf8Decoder::new(b);
    loop {
        match decoder.decode() {
            DecodeResult::EOF => {
                break;
            }
            DecodeResult::Error(e) => panic!(e),
            DecodeResult::Char(c) => {
                println!("{}", c);
            }
        }
    }
}