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

use std::str::FromStr;

mod char;
mod int;

pub use char::TryFromIntToCharError;
pub use int::TryFromIntError;

pub trait TryFrom<T>: Sized {
    type Err;
    fn try_from(T) -> Result<Self, Self::Err>;
}

pub trait TryInto<T>: Sized {
    type Err;
    fn try_into(self) -> Result<T, Self::Err>;
}

impl<T, U> TryInto<U> for T where U: TryFrom<T> {
    type Err = U::Err;
    fn try_into(self) -> Result<U, U::Err> {
        U::try_from(self)
    }
}

impl<'a, T> TryFrom<&'a str> for T where T: FromStr {
    type Err = T::Err;
    fn try_from(string: &'a str) -> Result<Self, Self::Err> {
        T::from_str(string)
    }
}

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

    #[test]
    fn should_have_try_from_impl_for_from_str() {
        let result = u32::try_from("3");
        assert_eq!(result.unwrap(), 3)
    }

    #[test]
    fn should_have_try_from_impl_for_from_str_that_handles_err() {
        let result = u32::try_from("hello");
        assert_eq!(format!("{}", result.unwrap_err()), "invalid digit found in string")
    }

    #[test]
    fn should_have_try_into_impl_for_from_str() {
        let result: Result<u32, _> = "3".try_into();
        assert_eq!(result.unwrap(), 3)
    }
}

/// Error type used when conversion is infallible.
/// The never type (`!`) will replace this when it is available in stable Rust.
#[derive(Debug, Eq, PartialEq)]
pub enum Void {}