use std::io::{self, stdin, Read};
use std::fs::File;
use std::env;

struct Input<R> {
    reader: R,
}

impl<'a, R> Read for Input<R> where R: Read {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        self.reader.read(buf)
    }
}

fn main() {
    let mut buffer = vec![0; 250];

    // Both File and StdinLock implements Read
    let mut reader = match env::args().nth(2) {
        Some(f) => Input{reader: File::open(f).expect("so bad")},
        None => Input{reader: {let stdin = stdin(); stdin.lock()}},
    };
    reader.read(&mut buffer).unwrap();
    println!("{:?}", buffer);
}