feat: Add type conversion and parsing exercises
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### Type conversions
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Rust offers a multitude of ways to convert a value of a given type into another type.
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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.
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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.
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The traits are the following:
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- `From` and `Into` covered in [`from_into`](from_into.rs)
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- `TryFrom` and `TryInto` covered in [`try_from_into`](try_from_into.rs)
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- `AsRef` and `AsMut` covered in [`as_ref_mut`](as_ref_mut.rs)
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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.
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These should be the main ways ***within the standard library*** to convert data into your desired types.
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#### Book Sections
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These are not directly covered in the book, but the standard library has great documentation for [conversions here](https://doc.rust-lang.org/std/convert/index.html). The `FromStr` trait is also covered [here](https://doc.rust-lang.org/std/str/trait.FromStr.html).
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// AsRef and AsMut allow for cheap reference-to-reference conversions.
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// Read more about them at https://doc.rust-lang.org/std/convert/trait.AsRef.html
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// and https://doc.rust-lang.org/std/convert/trait.AsMut.html, respectively.
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// Obtain the number of bytes (not characters) in the given argument
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// Add the AsRef trait appropriately as a trait bound
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fn byte_counter<T>(arg: T) -> usize {
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arg.as_ref().as_bytes().len()
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}
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// Obtain the number of characters (not bytes) in the given argument
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// Add the AsRef trait appropriately as a trait bound
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fn char_counter<T>(arg: T) -> usize {
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arg.as_ref().chars().collect::<Vec<_>>().len()
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}
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fn main() {
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let s = "Café au lait";
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println!("{}", char_counter(s));
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println!("{}", byte_counter(s));
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn different_counts() {
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let s = "Café au lait";
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assert_ne!(char_counter(s), byte_counter(s));
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}
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fn same_counts() {
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let s = "Cafe au lait";
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assert_eq!(char_counter(s), byte_counter(s));
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}
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}
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// The From trait is used for value-to-value conversions.
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// If From is implemented correctly for a type, the Into trait should work conversely.
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// You can read more about it at https://doc.rust-lang.org/std/convert/trait.From.html
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#[derive(Debug)]
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struct Person {
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name: String,
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age: usize,
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}
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// We implement the Default trait to use it as a fallback
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// when the provided string is not convertible into a Person object
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impl Default for Person {
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fn default() -> Person {
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Person {
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name: String::from("John"),
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age: 30,
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}
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}
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}
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// Your task is to complete this implementation
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// in order for the line `let p = Person::from("Mark,20")` to compile
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// Please note that you'll need to parse the age component into a `usize`
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// with something like `"4".parse::<usize>()`. The outcome of this needs to
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// be handled appropriately.
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//
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// Steps:
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// 1. If the length of the provided string is 0, then return the default of Person
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// 2. Split the given string on the commas present in it
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// 3. Extract the first element from the split operation and use it as the name
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// 4. Extract the other element from the split operation and parse it into a `usize` as the age
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// If while parsing the age, something goes wrong, then return the default of Person
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// Otherwise, then return an instantiated Person onject with the results
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impl From<&str> for Person {
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fn from(s: &str) -> Person {
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}
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}
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fn main() {
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// Use the `from` function
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let p1 = Person::from("Mark,20");
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// Since From is implemented for Person, we should be able to use Into
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let p2: Person = "Gerald,70".into();
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println!("{:?}", p1);
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println!("{:?}", p2);
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_default() {
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// Test that the default person is 30 year old John
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let dp = Person::default();
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assert_eq!(dp.name, "John");
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assert_eq!(dp.age, 30);
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}
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#[test]
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fn test_bad_convert() {
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// Test that John is returned when bad string is provided
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let p = Person::from("");
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assert_eq!(p.name, "John");
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assert_eq!(p.age, 30);
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}
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#[test]
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fn test_good_convert() {
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// Test that "Mark,20" works
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let p = Person::from("Mark,20");
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assert_eq!(p.name, "Mark");
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assert_eq!(p.age, 20);
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}
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}
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// This does practically the same thing that TryFrom<&str> does.
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// Additionally, upon implementing FromStr, you can use the `parse` method
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// on strings to generate an object of the implementor type.
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// You can read more about it at https://doc.rust-lang.org/std/str/trait.FromStr.html
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use std::str::FromStr;
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#[derive(Debug)]
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struct Person {
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name: String,
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age: usize,
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}
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// Steps:
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// 1. If the length of the provided string is 0, then return an error
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// 2. Split the given string on the commas present in it
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// 3. Extract the first element from the split operation and use it as the name
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// 4. Extract the other element from the split operation and parse it into a `usize` as the age
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// If while parsing the age, something goes wrong, then return an error
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// Otherwise, then return a Result of a Person object
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impl FromStr for Person {
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type Err = String;
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fn from_str(s: &str) -> Result<Person, Self::Err> {
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}
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}
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fn main() {
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let p = "Mark,20".parse::<Person>().unwrap();
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println!("{:?}", p);
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn empty_input() {
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assert!("".parse::<Person>().is_err());
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}
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#[test]
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fn good_input() {
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assert!("John,32".parse::<Person>().is_ok());
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}
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#[test]
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#[should_panic]
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fn missing_age() {
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"John".parse::<Person>().unwrap();
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}
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}
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// TryFrom is a simple and safe type conversion that may fail in a controlled way under some circumstances.
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// Basically, this is the same as From. The main difference is that this should return a Result type
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// instead of the target type itself.
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// You can read more about it at https://doc.rust-lang.org/std/convert/trait.TryFrom.html
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use std::convert::{TryInto, TryFrom};
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#[derive(Debug)]
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struct Person {
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name: String,
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age: usize,
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}
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// Your task is to complete this implementation
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// in order for the line `let p = Person::try_from("Mark,20")` to compile
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// and return an Ok result of inner type Person.
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// Please note that you'll need to parse the age component into a `usize`
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// with something like `"4".parse::<usize>()`. The outcome of this needs to
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// be handled appropriately.
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//
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// Steps:
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// 1. If the length of the provided string is 0, then return an error
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// 2. Split the given string on the commas present in it
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// 3. Extract the first element from the split operation and use it as the name
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// 4. Extract the other element from the split operation and parse it into a `usize` as the age
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// If while parsing the age, something goes wrong, then return an error
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// Otherwise, then return a Result of a Person object
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impl TryFrom<&str> for Person {
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type Error = String;
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fn try_from(s: &str) -> Result<Self, Self::Error> {
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}
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}
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fn main() {
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// Use the `from` function
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let p1 = Person::try_from("Mark,20");
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// Since From is implemented for Person, we should be able to use Into
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let p2: Result<Person, _> = "Gerald,70".try_into();
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println!("{:?}", p1);
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println!("{:?}", p2);
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_bad_convert() {
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// Test that John is returned when bad string is provided
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let p = Person::try_from("");
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assert!(p.is_err());
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}
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#[test]
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fn test_good_convert() {
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// Test that "Mark,20" works
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let p = Person::try_from("Mark,20");
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assert!(p.is_ok());
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let p = p.unwrap();
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assert_eq!(p.name, "Mark");
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assert_eq!(p.age, 20);
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}
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#[test]
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#[should_panic]
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fn test_panic_empty_input() {
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let p: Person = "".try_into().unwrap();
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}
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#[test]
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#[should_panic]
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fn test_panic_bad_age() {
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let p = Person::try_from("Mark,twenty").unwrap();
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}
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}
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// Type casting in Rust is done via the usage of the `as` operator.
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// Please note that the `as` operator is not only used when type casting.
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// It also helps with renaming imports.
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// The goal is to make sure that the division does not fail to compile
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fn average(values: &[f64]) -> f64 {
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let total = values
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.iter()
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.fold(0.0, |a, b| a + b);
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total / values.len()
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}
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fn main() {
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let values = [3.5, 0.3, 13.0, 11.7];
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println!("{}", average(&values));
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}
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40
info.toml
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info.toml
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@ -610,3 +610,43 @@ answers and don't understand why they work and yours doesn't.
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If you've learned from the sample solutions, I encourage you to come
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If you've learned from the sample solutions, I encourage you to come
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back to this exercise and try it again in a few days to reinforce
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back to this exercise and try it again in a few days to reinforce
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what you've learned :)"""
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what you've learned :)"""
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# TYPE CONVERSIONS
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[[exercises]]
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name = "using_as"
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path = "exercises/conversions/using_as.rs"
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mode = "compile"
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hint = """
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Use the `as` operator to cast one of the operands in the last line of the
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`average` function into the expected return type."""
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[[exercises]]
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name = "from_into"
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path = "exercises/conversions/from_into.rs"
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mode = "test"
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hint = """
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Follow the steps provided right before the `From` implementation"""
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[[exercises]]
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name = "try_from_into"
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path = "exercises/conversions/try_from_into.rs"
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mode = "test"
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hint = """
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Follow the steps provided right before the `From` implementation.
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You can also use the example at https://doc.rust-lang.org/std/convert/trait.TryFrom.html"""
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[[exercises]]
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name = "as_ref_mut"
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path = "exercises/conversions/as_ref_mut.rs"
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mode = "test"
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hint = """
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Add AsRef<str> as a trait bound to the functions."""
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[[exercises]]
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name = "from_str"
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path = "exercises/conversions/from_str.rs"
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mode = "test"
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hint = """
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If you've already solved try_from_into.rs, then this is almost a copy-paste.
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Otherwise, go ahead and solve try_from_into.rs first."""
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