rustlings/exercises/conversions/try_from_into.rs

// try_from_into.rs
// TryFrom is a simple and safe type conversion that may fail in a controlled way under some circumstances.
// Basically, this is the same as From. The main difference is that this should return a Result type
// instead of the target type itself.
// You can read more about it at https://doc.rust-lang.org/std/convert/trait.TryFrom.html
use std::convert::{TryFrom, TryInto};

#[derive(Debug, PartialEq)]
struct Color {
    red: u8,
    green: u8,
    blue: u8,
}

// We will use this error type for these `TryFrom` conversions.
#[derive(Debug, PartialEq)]
enum IntoColorError {
    // Incorrect length of slice
    BadLen,
    // Integer conversion error
    IntConversion,
}

// Your task is to complete this implementation
// and return an Ok result of inner type Color.
// You need to create an implementation for a tuple of three integers,
// an array of three integers, and a slice of integers.
//
// Note that the implementation for tuple and array will be checked at compile time,
// but the slice implementation needs to check the slice length!
// Also note that correct RGB color values must be integers in the 0..=255 range.

// Tuple implementation
impl TryFrom<(i16, i16, i16)> for Color {
    type Error = IntoColorError;
    fn try_from(tuple: (i16, i16, i16)) -> Result<Self, Self::Error> {
        let red = if tuple.0 >= 0 && tuple.0 <= 255 {
            tuple.0 as u8
        } else {
            return Err(Self::Error::IntConversion);
        };

        let green = if tuple.1 >= 0 && tuple.1 <= 255 {
            tuple.1 as u8
        } else {
            return Err(Self::Error::IntConversion);
        };

        let blue = if tuple.2 >= 0 && tuple.2 <= 255 {
            tuple.2 as u8
        } else {
            return Err(Self::Error::IntConversion);
        };

        Ok(Color { red, green, blue })
    }
}

// Array implementation
impl TryFrom<[i16; 3]> for Color {
    type Error = IntoColorError;
    fn try_from(arr: [i16; 3]) -> Result<Self, Self::Error> {
        let red = if arr[0] >= 0 && arr[0] <= 255 {
            arr[0] as u8
        } else {
            return Err(Self::Error::IntConversion);
        };

        let green = if arr[1] >= 0 && arr[1] <= 255 {
            arr[1] as u8
        } else {
            return Err(Self::Error::IntConversion);
        };

        let blue = if arr[2] >= 0 && arr[2] <= 255 {
            arr[2] as u8
        } else {
            return Err(Self::Error::IntConversion);
        };

        Ok(Color { red, green, blue })
    }
}

// Slice implementation
impl TryFrom<&[i16]> for Color {
    type Error = IntoColorError;
    fn try_from(slice: &[i16]) -> Result<Self, Self::Error> {

        if slice.len() != 3 {
            return Err(Self::Error::BadLen);
        }

        let red = if slice[0] >= 0 && slice[0] <= 255 {
            slice[0] as u8
        } else {
            return Err(Self::Error::IntConversion);
        };

        let green = if slice[1] >= 0 && slice[1] <= 255 {
            slice[1] as u8
        } else {
            return Err(Self::Error::IntConversion);
        };

        let blue = if slice[2] >= 0 && slice[2] <= 255 {
            slice[2] as u8
        } else {
            return Err(Self::Error::IntConversion);
        };

        Ok(Color { red, green, blue })
    }
}

fn main() {
    // Use the `from` function
    let c1 = Color::try_from((183, 65, 14));
    println!("{:?}", c1);

    // Since TryFrom is implemented for Color, we should be able to use TryInto
    let c2: Result<Color, _> = [183, 65, 14].try_into();
    println!("{:?}", c2);

    let v = vec![183, 65, 14];
    // With slice we should use `try_from` function
    let c3 = Color::try_from(&v[..]);
    println!("{:?}", c3);
    // or take slice within round brackets and use TryInto
    let c4: Result<Color, _> = (&v[..]).try_into();
    println!("{:?}", c4);
}

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

    #[test]
    fn test_tuple_out_of_range_positive() {
        assert_eq!(
            Color::try_from((256, 1000, 10000)),
            Err(IntoColorError::IntConversion)
        );
    }
    #[test]
    fn test_tuple_out_of_range_negative() {
        assert_eq!(
            Color::try_from((-1, -10, -256)),
            Err(IntoColorError::IntConversion)
        );
    }
    #[test]
    fn test_tuple_sum() {
        assert_eq!(
            Color::try_from((-1, 255, 255)),
            Err(IntoColorError::IntConversion)
        );
    }
    #[test]
    fn test_tuple_correct() {
        let c: Result<Color, _> = (183, 65, 14).try_into();
        assert!(c.is_ok());
        assert_eq!(
            c.unwrap(),
            Color {
                red: 183,
                green: 65,
                blue: 14
            }
        );
    }
    #[test]
    fn test_array_out_of_range_positive() {
        let c: Result<Color, _> = [1000, 10000, 256].try_into();
        assert_eq!(c, Err(IntoColorError::IntConversion));
    }
    #[test]
    fn test_array_out_of_range_negative() {
        let c: Result<Color, _> = [-10, -256, -1].try_into();
        assert_eq!(c, Err(IntoColorError::IntConversion));
    }
    #[test]
    fn test_array_sum() {
        let c: Result<Color, _> = [-1, 255, 255].try_into();
        assert_eq!(c, Err(IntoColorError::IntConversion));
    }
    #[test]
    fn test_array_correct() {
        let c: Result<Color, _> = [183, 65, 14].try_into();
        assert!(c.is_ok());
        assert_eq!(
            c.unwrap(),
            Color {
                red: 183,
                green: 65,
                blue: 14
            }
        );
    }
    #[test]
    fn test_slice_out_of_range_positive() {
        let arr = [10000, 256, 1000];
        assert_eq!(
            Color::try_from(&arr[..]),
            Err(IntoColorError::IntConversion)
        );
    }
    #[test]
    fn test_slice_out_of_range_negative() {
        let arr = [-256, -1, -10];
        assert_eq!(
            Color::try_from(&arr[..]),
            Err(IntoColorError::IntConversion)
        );
    }
    #[test]
    fn test_slice_sum() {
        let arr = [-1, 255, 255];
        assert_eq!(
            Color::try_from(&arr[..]),
            Err(IntoColorError::IntConversion)
        );
    }
    #[test]
    fn test_slice_correct() {
        let v = vec![183, 65, 14];
        let c: Result<Color, _> = Color::try_from(&v[..]);
        assert!(c.is_ok());
        assert_eq!(
            c.unwrap(),
            Color {
                red: 183,
                green: 65,
                blue: 14
            }
        );
    }
    #[test]
    fn test_slice_excess_length() {
        let v = vec![0, 0, 0, 0];
        assert_eq!(Color::try_from(&v[..]), Err(IntoColorError::BadLen));
    }
    #[test]
    fn test_slice_insufficient_length() {
        let v = vec![0, 0];
        assert_eq!(Color::try_from(&v[..]), Err(IntoColorError::BadLen));
    }
}