[rustlings]23_conversions

from_into.rs

// The `From` trait is used for value-to-value conversions. If `From` is
// implemented, an implementation of `Into` is automatically provided.
// You can read more about it in the documentation:
// https://doc.rust-lang.org/std/convert/trait.From.html

#[derive(Debug)]
struct Person {
    name: String,
    age: u8,
}

// We implement the Default trait to use it as a fallback when the provided
// string is not convertible into a `Person` object.
impl Default for Person {
    fn default() -> Self {
        Self {
            name: String::from("John"),
            age: 30,
        }
    }
}

// TODO: Complete this `From` implementation to be able to parse a `Person`
// out of a string in the form of "Mark,20".
// Note that you'll need to parse the age component into a `u8` with something
// like `"4".parse::<u8>()`.
//
// Steps:
// 1. Split the given string on the commas present in it.
// 2. If the split operation returns less or more than 2 elements, return the
//    default of `Person`.
// 3. Use the first element from the split operation as the name.
// 4. If the name is empty, return the default of `Person`.
// 5. Parse the second element from the split operation into a `u8` as the age.
// 6. If parsing the age fails, return the default of `Person`.
impl From<&str> for Person {
    fn from(s: &str) -> Self {
        let (name, age) = match s.split_once(',') {
            Some((name, age)) => (name.trim(), age.trim()),
            _ => return Person::default(),
        };

        if let Ok(age) = age.parse::<usize>() {
            if !name.is_empty() {
                return Person {
                    name: String::from(name),
                    age:age.try_into().unwrap(),
                };
            }
        }
        Person::default()
    }
}

fn main() {
    // Use the `from` function.
    let p1 = Person::from("Mark,20");
    println!("{p1:?}");

    // Since `From` is implemented for Person, we are able to use `Into`.
    let p2: Person = "Gerald,70".into();
    println!("{p2:?}");
}

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

    #[test]
    fn test_default() {
        let dp = Person::default();
        assert_eq!(dp.name, "John");
        assert_eq!(dp.age, 30);
    }

    #[test]
    fn test_bad_convert() {
        let p = Person::from("");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_good_convert() {
        let p = Person::from("Mark,20");
        assert_eq!(p.name, "Mark");
        assert_eq!(p.age, 20);
    }

    #[test]
    fn test_bad_age() {
        let p = Person::from("Mark,twenty");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_missing_comma_and_age() {
        let p: Person = Person::from("Mark");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_missing_age() {
        let p: Person = Person::from("Mark,");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_missing_name() {
        let p: Person = Person::from(",1");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_missing_name_and_age() {
        let p: Person = Person::from(",");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_missing_name_and_invalid_age() {
        let p: Person = Person::from(",one");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_trailing_comma() {
        let p: Person = Person::from("Mike,32,");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }

    #[test]
    fn test_trailing_comma_and_some_string() {
        let p: Person = Person::from("Mike,32,dog");
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 30);
    }
}

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from_str.rs

// This is similar to the previous `from_into` exercise. But this time, we'll
// implement `FromStr` and return errors instead of falling back to a default
// value. Additionally, upon implementing `FromStr`, you can use the `parse`
// method on strings to generate an object of the implementor type. You can read
// more about it in the documentation:
// https://doc.rust-lang.org/std/str/trait.FromStr.html

use std::num::ParseIntError;
use std::str::FromStr;

#[derive(Debug, PartialEq)]
struct Person {
    name: String,
    age: u8,
}

// We will use this error type for the `FromStr` implementation.
#[derive(Debug, PartialEq)]
enum ParsePersonError {
    // Incorrect number of fields
    BadLen,
    // Empty name field
    NoName,
    // Wrapped error from parse::<u8>()
    ParseInt(ParseIntError),
}

// TODO: Complete this `From` implementation to be able to parse a `Person`
// out of a string in the form of "Mark,20".
// Note that you'll need to parse the age component into a `u8` with something
// like `"4".parse::<u8>()`.
//
// Steps:
// 1. Split the given string on the commas present in it.
// 2. If the split operation returns less or more than 2 elements, return the
//    error `ParsePersonError::BadLen`.
// 3. Use the first element from the split operation as the name.
// 4. If the name is empty, return the error `ParsePersonError::NoName`.
// 5. Parse the second element from the split operation into a `u8` as the age.
// 6. If parsing the age fails, return the error `ParsePersonError::ParseInt`.
impl FromStr for Person {
    type Err = ParsePersonError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        if s.is_empty() {
            return Err(ParsePersonError::BadLen);
        }
        let splitted_item = s.split(',').collect::<Vec<&str>>();
        let (name, age) = match &splitted_item[..] {
            [name, age] => (
                name.to_string(),
                age.parse().map_err(ParsePersonError::ParseInt)?,
            ),
            _ => return Err(ParsePersonError::BadLen),
        };
        if name.is_empty() {
            return Err(ParsePersonError::NoName);
        }

        Ok(Person {
            name,
            age,
        })
    }
}

fn main() {
    let p = "Mark,20".parse::<Person>();
    println!("{p:?}");
}

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

    #[test]
    fn empty_input() {
        assert_eq!("".parse::<Person>(), Err(BadLen));
    }

    #[test]
    fn good_input() {
        let p = "John,32".parse::<Person>();
        assert!(p.is_ok());
        let p = p.unwrap();
        assert_eq!(p.name, "John");
        assert_eq!(p.age, 32);
    }

    #[test]
    fn missing_age() {
        assert!(matches!("John,".parse::<Person>(), Err(ParseInt(_))));
    }

    #[test]
    fn invalid_age() {
        assert!(matches!("John,twenty".parse::<Person>(), Err(ParseInt(_))));
    }

    #[test]
    fn missing_comma_and_age() {
        assert_eq!("John".parse::<Person>(), Err(BadLen));
    }

    #[test]
    fn missing_name() {
        assert_eq!(",1".parse::<Person>(), Err(NoName));
    }

    #[test]
    fn missing_name_and_age() {
        assert!(matches!(",".parse::<Person>(), Err(NoName | ParseInt(_))));
    }

    #[test]
    fn missing_name_and_invalid_age() {
        assert!(matches!(
            ",one".parse::<Person>(),
            Err(NoName | ParseInt(_)),
        ));
    }

    #[test]
    fn trailing_comma() {
        assert_eq!("John,32,".parse::<Person>(), Err(BadLen));
    }

    #[test]
    fn trailing_comma_and_some_string() {
        assert_eq!("John,32,man".parse::<Person>(), Err(BadLen));
    }
}


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as_ref_mut.rs

// AsRef and AsMut allow for cheap reference-to-reference conversions. Read more
// about them at https://doc.rust-lang.org/std/convert/trait.AsRef.html and
// https://doc.rust-lang.org/std/convert/trait.AsMut.html, respectively.

// Obtain the number of bytes (not characters) in the given argument.
// TODO: Add the `AsRef` trait appropriately as a trait bound.
fn byte_counter<T: AsRef<str>>(arg: T) -> usize {
    arg.as_ref().as_bytes().len()
}

// Obtain the number of characters (not bytes) in the given argument.
// TODO: Add the `AsRef` trait appropriately as a trait bound.
fn char_counter<T: AsRef<str>>(arg: T) -> usize {
    arg.as_ref().chars().count()
}

// Squares a number using `as_mut()`.
// TODO: Add the appropriate trait bound.
fn num_sq<T: AsMut<u32>>(arg: &mut T) {
    // TODO: Implement the function body.
    *arg.as_mut() *= *arg.as_mut()
}

fn main() {
    // You can optionally experiment here.
}

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

    #[test]
    fn different_counts() {
        let s = "Café au lait";
        assert_ne!(char_counter(s), byte_counter(s));
    }

    #[test]
    fn same_counts() {
        let s = "Cafe au lait";
        assert_eq!(char_counter(s), byte_counter(s));
    }

    #[test]
    fn different_counts_using_string() {
        let s = String::from("Café au lait");
        assert_ne!(char_counter(s.clone()), byte_counter(s));
    }

    #[test]
    fn same_counts_using_string() {
        let s = String::from("Cafe au lait");
        assert_eq!(char_counter(s.clone()), byte_counter(s));
    }

    #[test]
    fn mut_box() {
        let mut num: Box<u32> = Box::new(3);
        num_sq(&mut num);
        assert_eq!(*num, 9);
    }
}

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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 in the documentation:
// https://doc.rust-lang.org/std/convert/trait.TryFrom.html

#![allow(clippy::useless_vec)]
use std::convert::{TryFrom, TryInto};

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

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

// TODO: Tuple implementation.
// Correct RGB color values must be integers in the 0..=255 range.
impl TryFrom<(i16, i16, i16)> for Color {
    type Error = IntoColorError;

    fn try_from(tuple: (i16, i16, i16)) -> Result<Self, Self::Error> {
        let (red, green, blue) = tuple;

        for color in [red, green, blue] {
            if !(0..=255).contains(&color) {
                return Err(IntoColorError::IntConversion);
            }
        }
        Ok(Self {
            red: tuple.0 as u8,
            green: tuple.1 as u8,
            blue: tuple.2 as u8,
        })
    }
}

// TODO: Array implementation.
impl TryFrom<[i16; 3]> for Color {
    type Error = IntoColorError;

    fn try_from(arr: [i16; 3]) -> Result<Self, Self::Error> {
        for color in arr {
            if !(0..=255).contains(&color) {
                return Err(IntoColorError::IntConversion);
            }
        }
        Ok(Self {
            red: arr[0] as u8,
            green: arr[1] as u8,
            blue: arr[2] as u8,
        })
    }
}

// TODO: Slice implementation.
// This implementation needs to check the slice length.
impl TryFrom<&[i16]> for Color {
    type Error = IntoColorError;

    fn try_from(slice: &[i16]) -> Result<Self, Self::Error> {
        if slice.len() != 3 {
            return Err(IntoColorError::BadLen);
        }
        for color in slice {
            if !(0..=255).contains(color) {
                return Err(IntoColorError::IntConversion);
            }
        }
        Ok(Self {
            red: slice[0] as u8,
            green: slice[1] as u8,
            blue: slice[2] as u8,
        })
    }
}

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

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

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

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

    #[test]
    fn test_tuple_out_of_range_positive() {
        assert_eq!(Color::try_from((256, 1000, 10000)), Err(IntConversion));
    }

    #[test]
    fn test_tuple_out_of_range_negative() {
        assert_eq!(Color::try_from((-1, -10, -256)), Err(IntConversion));
    }

    #[test]
    fn test_tuple_sum() {
        assert_eq!(Color::try_from((-1, 255, 255)), Err(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(IntConversion));
    }

    #[test]
    fn test_array_out_of_range_negative() {
        let c: Result<Color, _> = [-10, -256, -1].try_into();
        assert_eq!(c, Err(IntConversion));
    }

    #[test]
    fn test_array_sum() {
        let c: Result<Color, _> = [-1, 255, 255].try_into();
        assert_eq!(c, Err(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(IntConversion));
    }

    #[test]
    fn test_slice_out_of_range_negative() {
        let arr = [-256, -1, -10];
        assert_eq!(Color::try_from(&arr[..]), Err(IntConversion));
    }

    #[test]
    fn test_slice_sum() {
        let arr = [-1, 255, 255];
        assert_eq!(Color::try_from(&arr[..]), Err(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(BadLen));
    }

    #[test]
    fn test_slice_insufficient_length() {
        let v = vec![0, 0];
        assert_eq!(Color::try_from(&v[..]), Err(BadLen));
    }
}

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