Function tweetr::util::prompt_exact_len

pub fn prompt_exact_len<R, W, F>(
    input: &mut R, 
    output: &mut W, 
    prompt_s: &str, 
    verifier: F, 
    desired_len: usize
) -> IoResult<String> where
    R: BufRead,
    W: Write,
    F: Fn(&String) -> bool, 

Ask the user to input a string of the exact length of desired_len, (re)prompting as necessary.

Examples

Allow anything 10 charactes long:

assert_eq!(prompt_exact_len(&mut Cursor::new(b"0123456789"),
                            &mut Vec::new(),
                            "Allowed chars",
                            |_| true,
                            10).unwrap(),
           "0123456789".to_string());

Allow a 10-character-long u64:

assert_eq!(prompt_exact_len(&mut Cursor::new(b"1234567890"),
                            &mut Vec::new(),
                            "Long number",
                            |s| u64::from_str(s).is_ok(),
                            10).unwrap(),
           "1234567890".to_string());
assert!(prompt_exact_len(&mut Cursor::new(b"1234abcdef"),
                         &mut Vec::new(),
                         "Long number",
                         |s| u64::from_str(s).is_ok(),
                         10).is_err());