1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112

use std::fmt;
use std::io;

use crate::PascalString;

pub trait DisplayExt {
    fn is_empty(&self) -> bool;

    fn write_to_fmt<W: fmt::Write>(&self, writer: W) -> fmt::Result;

    fn write_to_bytes<W: io::Write>(&self, writer: W) -> fmt::Result;

    fn try_to_fmt<T: fmt::Write + Default>(&self) -> Result<T, T> {
        let mut writer = T::default();
        match self.write_to_fmt(&mut writer) {
            Ok(_) => Ok(writer),
            Err(_err) => Err(writer),
        }
    }

    fn try_to_bytes<T: io::Write + Default>(&self) -> Result<T, T> {
        let mut writer = T::default();
        match self.write_to_bytes(&mut writer) {
            Ok(_) => Ok(writer),
            Err(_err) => Err(writer),
        }
    }

    fn to_fmt<T: fmt::Write + Default>(&self) -> T {
        self.try_to_fmt()
            .unwrap_or_else(|_writer| panic!("Failed to write to target"))
    }

    fn to_bytes<T: io::Write + Default>(&self) -> T {
        self.try_to_bytes()
            .unwrap_or_else(|_writer| panic!("Failed to write to target"))
    }
}

impl<T> DisplayExt for T
where
    T: fmt::Display + ?Sized,
{
    fn is_empty(&self) -> bool {
        self.write_to_fmt(PascalString::<0>::new()).is_ok()
    }

    fn write_to_fmt<W: fmt::Write>(&self, mut writer: W) -> fmt::Result {
        write!(writer, "{}", self)
    }

    fn write_to_bytes<W: io::Write>(&self, mut writer: W) -> fmt::Result {
        writer
            .write_fmt(format_args!("{}", self))
            .map_err(|_| fmt::Error)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    struct Maybe<T>(Option<T>);

    impl<T: fmt::Display> fmt::Display for Maybe<T> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            if let Some(t) = &self.0 {
                t.fmt(f)?
            }
            Ok(())
        }
    }

    fn is_empty(display: impl fmt::Display) -> bool {
        display.is_empty()
    }

    #[test]
    fn test_is_empty() {
        assert!(is_empty(""));
        assert!(!is_empty("Hello"));

        assert!(is_empty("".to_string()));
        assert!(!is_empty("Hello".to_string()));

        assert!(is_empty(&"" as &dyn fmt::Display));
        assert!(!is_empty(&"Hello" as &dyn fmt::Display));

        assert!(is_empty(&"".to_string() as &dyn fmt::Display));
        assert!(!is_empty(&"Hello".to_string() as &dyn fmt::Display));

        assert!(is_empty(Maybe(None::<&str>)));
        assert!(is_empty(Maybe(Some(""))));
        assert!(!is_empty(Maybe(Some("Hello"))));
    }

    #[test]
    fn test_to_fmt() {
        assert_eq!("".to_fmt::<PascalString<0>>(), "");
        assert_eq!("", "".to_fmt::<PascalString<0>>());
        assert_eq!("Hello", "Hello".to_fmt::<PascalString<255>>());
        assert_eq!("Hello", "Hello".try_to_fmt::<PascalString<255>>().unwrap());
        assert!("".try_to_fmt::<PascalString<4>>().is_ok());
        assert!("Hello".try_to_fmt::<PascalString<4>>().is_err());
    }

    #[test]
    #[should_panic]
    fn test_to_fmt_panic() {
        "Hello".to_fmt::<PascalString<4>>();
    }
}