Doc's example code for BufferedWriter is wrong and also generate warnings

[jameschurchman]

Struct std::io::BufferedWriter has the example code :

use std::io::{BufferedWriter, File};

let file = File::open(&Path::new("message.txt"));
let mut writer = BufferedWriter::new(file);

writer.write_str("hello, world");
writer.flush();

But this code opens the file as read only, it should open it for writing or creating a new file, for example :

let file = File::create(&Path::new("message.txt"));

It also generates two warnings :

buff_writer.rs:7:2: 7:35 warning: unused result which must be used, #[warn(unused_must_use)] on by default
buff_writer.rs:7    writer.write_str("hello, world");
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
buff_writer.rs:8:2: 8:17 warning: unused result which must be used, #[warn(unused_must_use)] on by default
buff_writer.rs:8    writer.flush();

by unwrap()ing both these remove the errors, and in the case where File::open is used to successfully crash the sample app when attempting to append to a read only file.

[steveklabnik]

So the reasons that the warnings don't happen is

/// ```rust
/// # #![allow(unused_must_use)]
/// use std::io::{BufferedWriter, File};
///
/// let file = File::open(&Path::new("message.txt"));
/// let mut writer = BufferedWriter::new(file);
///
/// writer.write_str("hello, world");
/// writer.flush();
/// ```

They were turned off!