Update Exercises Directory Names to Reflect Order

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diff --git a/exercises/23_conversions/README.md b/exercises/23_conversions/README.md
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+# Type conversions
+
+Rust offers a multitude of ways to convert a value of a given type into another type.
+
+The simplest form of type conversion is a type cast expression. It is denoted with the binary operator `as`. For instance, `println!("{}", 1 + 1.0);` would not compile, since `1` is an integer while `1.0` is a float. However, `println!("{}", 1 as f32 + 1.0)` should compile. The exercise [`using_as`](using_as.rs) tries to cover this.
+
+Rust also offers traits that facilitate type conversions upon implementation. These traits can be found under the [`convert`](https://doc.rust-lang.org/std/convert/index.html) module.
+The traits are the following:
+
+- `From` and `Into` covered in [`from_into`](from_into.rs)
+- `TryFrom` and `TryInto` covered in [`try_from_into`](try_from_into.rs)
+- `AsRef` and `AsMut` covered in [`as_ref_mut`](as_ref_mut.rs)
+
+Furthermore, the `std::str` module offers a trait called [`FromStr`](https://doc.rust-lang.org/std/str/trait.FromStr.html) which helps with converting strings into target types via the `parse` method on strings. If properly implemented for a given type `Person`, then `let p: Person = "Mark,20".parse().unwrap()` should both compile and run without panicking.
+
+These should be the main ways ***within the standard library*** to convert data into your desired types.
+
+## Further information
+
+These are not directly covered in the book, but the standard library has a great documentation for it.
+
+- [conversions](https://doc.rust-lang.org/std/convert/index.html)
+- [`FromStr` trait](https://doc.rust-lang.org/std/str/trait.FromStr.html)
diff --git a/exercises/23_conversions/as_ref_mut.rs b/exercises/23_conversions/as_ref_mut.rs
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+++ b/exercises/23_conversions/as_ref_mut.rs
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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.
+//
+// Execute `rustlings hint as_ref_mut` or use the `hint` watch subcommand for a
+// hint.
+
+// I AM NOT DONE
+
+// 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>(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>(arg: T) -> usize {
+    arg.as_ref().chars().count()
+}
+
+// Squares a number using as_mut().
+// TODO: Add the appropriate trait bound.
+fn num_sq<T>(arg: &mut T) {
+    // TODO: Implement the function body.
+    ???
+}
+
+#[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);
+    }
+}
diff --git a/exercises/23_conversions/from_into.rs b/exercises/23_conversions/from_into.rs
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+++ b/exercises/23_conversions/from_into.rs
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+// from_into.rs
+//
+// The From trait is used for value-to-value conversions. If From is implemented
+// correctly for a type, the Into trait should work conversely. You can read
+// more about it at https://doc.rust-lang.org/std/convert/trait.From.html
+//
+// Execute `rustlings hint from_into` or use the `hint` watch subcommand for a
+// hint.
+
+#[derive(Debug)]
+struct Person {
+    name: String,
+    age: usize,
+}
+
+// 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() -> Person {
+        Person {
+            name: String::from("John"),
+            age: 30,
+        }
+    }
+}
+
+// Your task is to complete this implementation in order for the line `let p =
+// Person::from("Mark,20")` to compile Please note that you'll need to parse the
+// age component into a `usize` with something like `"4".parse::<usize>()`. The
+// outcome of this needs to be handled appropriately.
+//
+// Steps:
+// 1. If the length of the provided string is 0, then return the default of
+//    Person.
+// 2. Split the given string on the commas present in it.
+// 3. Extract the first element from the split operation and use it as the name.
+// 4. If the name is empty, then return the default of Person.
+// 5. Extract the other element from the split operation and parse it into a
+//    `usize` as the age.
+// If while parsing the age, something goes wrong, then return the default of
+// Person Otherwise, then return an instantiated Person object with the results
+
+// I AM NOT DONE
+
+impl From<&str> for Person {
+    fn from(s: &str) -> Person {
+    }
+}
+
+fn main() {
+    // Use the `from` function
+    let p1 = Person::from("Mark,20");
+    // Since From is implemented for Person, we should be able to use Into
+    let p2: Person = "Gerald,70".into();
+    println!("{:?}", p1);
+    println!("{:?}", p2);
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_default() {
+        // Test that the default person is 30 year old John
+        let dp = Person::default();
+        assert_eq!(dp.name, "John");
+        assert_eq!(dp.age, 30);
+    }
+    #[test]
+    fn test_bad_convert() {
+        // Test that John is returned when bad string is provided
+        let p = Person::from("");
+        assert_eq!(p.name, "John");
+        assert_eq!(p.age, 30);
+    }
+    #[test]
+    fn test_good_convert() {
+        // Test that "Mark,20" works
+        let p = Person::from("Mark,20");
+        assert_eq!(p.name, "Mark");
+        assert_eq!(p.age, 20);
+    }
+    #[test]
+    fn test_bad_age() {
+        // Test that "Mark,twenty" will return the default person due to an
+        // error in parsing 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, "Mike");
+        assert_eq!(p.age, 32);
+    }
+
+    #[test]
+    fn test_trailing_comma_and_some_string() {
+        let p: Person = Person::from("Mike,32,man");
+        assert_eq!(p.name, "Mike");
+        assert_eq!(p.age, 32);
+    }
+}
diff --git a/exercises/23_conversions/from_str.rs b/exercises/23_conversions/from_str.rs
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+++ b/exercises/23_conversions/from_str.rs
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+// from_str.rs
+//
+// This is similar to from_into.rs, 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 at
+// https://doc.rust-lang.org/std/str/trait.FromStr.html
+//
+// Execute `rustlings hint from_str` or use the `hint` watch subcommand for a
+// hint.
+
+use std::num::ParseIntError;
+use std::str::FromStr;
+
+#[derive(Debug, PartialEq)]
+struct Person {
+    name: String,
+    age: usize,
+}
+
+// We will use this error type for the `FromStr` implementation.
+#[derive(Debug, PartialEq)]
+enum ParsePersonError {
+    // Empty input string
+    Empty,
+    // Incorrect number of fields
+    BadLen,
+    // Empty name field
+    NoName,
+    // Wrapped error from parse::<usize>()
+    ParseInt(ParseIntError),
+}
+
+// I AM NOT DONE
+
+// Steps:
+// 1. If the length of the provided string is 0, an error should be returned
+// 2. Split the given string on the commas present in it
+// 3. Only 2 elements should be returned from the split, otherwise return an
+//    error
+// 4. Extract the first element from the split operation and use it as the name
+// 5. Extract the other element from the split operation and parse it into a
+//    `usize` as the age with something like `"4".parse::<usize>()`
+// 6. If while extracting the name and the age something goes wrong, an error
+//    should be returned
+// If everything goes well, then return a Result of a Person object
+//
+// As an aside: `Box<dyn Error>` implements `From<&'_ str>`. This means that if
+// you want to return a string error message, you can do so via just using
+// return `Err("my error message".into())`.
+
+impl FromStr for Person {
+    type Err = ParsePersonError;
+    fn from_str(s: &str) -> Result<Person, Self::Err> {
+    }
+}
+
+fn main() {
+    let p = "Mark,20".parse::<Person>().unwrap();
+    println!("{:?}", p);
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn empty_input() {
+        assert_eq!("".parse::<Person>(), Err(ParsePersonError::Empty));
+    }
+    #[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(ParsePersonError::ParseInt(_))
+        ));
+    }
+
+    #[test]
+    fn invalid_age() {
+        assert!(matches!(
+            "John,twenty".parse::<Person>(),
+            Err(ParsePersonError::ParseInt(_))
+        ));
+    }
+
+    #[test]
+    fn missing_comma_and_age() {
+        assert_eq!("John".parse::<Person>(), Err(ParsePersonError::BadLen));
+    }
+
+    #[test]
+    fn missing_name() {
+        assert_eq!(",1".parse::<Person>(), Err(ParsePersonError::NoName));
+    }
+
+    #[test]
+    fn missing_name_and_age() {
+        assert!(matches!(
+            ",".parse::<Person>(),
+            Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_))
+        ));
+    }
+
+    #[test]
+    fn missing_name_and_invalid_age() {
+        assert!(matches!(
+            ",one".parse::<Person>(),
+            Err(ParsePersonError::NoName | ParsePersonError::ParseInt(_))
+        ));
+    }
+
+    #[test]
+    fn trailing_comma() {
+        assert_eq!("John,32,".parse::<Person>(), Err(ParsePersonError::BadLen));
+    }
+
+    #[test]
+    fn trailing_comma_and_some_string() {
+        assert_eq!(
+            "John,32,man".parse::<Person>(),
+            Err(ParsePersonError::BadLen)
+        );
+    }
+}
diff --git a/exercises/23_conversions/try_from_into.rs b/exercises/23_conversions/try_from_into.rs
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+++ b/exercises/23_conversions/try_from_into.rs
@@ -0,0 +1,193 @@
+// 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
+//
+// Execute `rustlings hint try_from_into` or use the `hint` watch subcommand for
+// a hint.
+
+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,
+}
+
+// I AM NOT DONE
+
+// 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> {
+    }
+}
+
+// Array implementation
+impl TryFrom<[i16; 3]> for Color {
+    type Error = IntoColorError;
+    fn try_from(arr: [i16; 3]) -> Result<Self, Self::Error> {
+    }
+}
+
+// Slice implementation
+impl TryFrom<&[i16]> for Color {
+    type Error = IntoColorError;
+    fn try_from(slice: &[i16]) -> Result<Self, Self::Error> {
+    }
+}
+
+fn main() {
+    // Use the `try_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));
+    }
+}
diff --git a/exercises/23_conversions/using_as.rs b/exercises/23_conversions/using_as.rs
new file mode 100644
index 0000000..414cef3
--- /dev/null
+++ b/exercises/23_conversions/using_as.rs
@@ -0,0 +1,33 @@
+// using_as.rs
+//
+// Type casting in Rust is done via the usage of the `as` operator. Please note
+// that the `as` operator is not only used when type casting. It also helps with
+// renaming imports.
+//
+// The goal is to make sure that the division does not fail to compile and
+// returns the proper type.
+//
+// Execute `rustlings hint using_as` or use the `hint` watch subcommand for a
+// hint.
+
+// I AM NOT DONE
+
+fn average(values: &[f64]) -> f64 {
+    let total = values.iter().sum::<f64>();
+    total / values.len()
+}
+
+fn main() {
+    let values = [3.5, 0.3, 13.0, 11.7];
+    println!("{}", average(&values));
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn returns_proper_type_and_value() {
+        assert_eq!(average(&[3.5, 0.3, 13.0, 11.7]), 7.125);
+    }
+}