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481 lines
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<main>
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<h1 id="associated-functions--methods"><a class="header" href="#associated-functions--methods">Associated functions & Methods</a></h1>
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<h2 id="examples"><a class="header" href="#examples">Examples</a></h2>
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<pre><pre class="playground"><code class="language-rust editable edition2021">struct Point {
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x: f64,
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y: f64,
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}
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// Implementation block, all `Point` associated functions & methods go in here.
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impl Point {
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// This is an "associated function" because this function is associated with
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// a particular type, that is, Point.
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//
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// Associated functions don't need to be called with an instance.
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// These functions are generally used like constructors.
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fn origin() -> Point {
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Point { x: 0.0, y: 0.0 }
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}
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// Another associated function, taking two arguments:
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fn new(x: f64, y: f64) -> Point {
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Point { x: x, y: y }
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}
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}
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struct Rectangle {
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p1: Point,
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p2: Point,
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}
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impl Rectangle {
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// This is a method.
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// `&self` is sugar for `self: &Self`, where `Self` is the type of the
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// caller object. In this case `Self` = `Rectangle`
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fn area(&self) -> f64 {
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// `self` gives access to the struct fields via the dot operator.
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let Point { x: x1, y: y1 } = self.p1;
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let Point { x: x2, y: y2 } = self.p2;
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// `abs` is a `f64` method that returns the absolute value of the
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// caller
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((x1 - x2) * (y1 - y2)).abs()
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}
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fn perimeter(&self) -> f64 {
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let Point { x: x1, y: y1 } = self.p1;
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let Point { x: x2, y: y2 } = self.p2;
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2.0 * ((x1 - x2).abs() + (y1 - y2).abs())
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}
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// This method requires the caller object to be mutable
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// `&mut self` desugars to `self: &mut Self`
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fn translate(&mut self, x: f64, y: f64) {
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self.p1.x += x;
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self.p2.x += x;
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self.p1.y += y;
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self.p2.y += y;
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}
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}
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// `Pair` owns resources: two heap allocated integers.
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struct Pair(Box<i32>, Box<i32>);
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impl Pair {
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// This method "consumes" the resources of the caller object
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// `self` desugars to `self: Self`
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fn destroy(self) {
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// Destructure `self`
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let Pair(first, second) = self;
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println!("Destroying Pair({}, {})", first, second);
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// `first` and `second` go out of scope and get freed.
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}
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}
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fn main() {
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let rectangle = Rectangle {
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// Associated functions are called using double colons
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p1: Point::origin(),
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p2: Point::new(3.0, 4.0),
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};
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// Methods are called using the dot operator.
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// Note that the first argument `&self` is implicitly passed, i.e.
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// `rectangle.perimeter()` === `Rectangle::perimeter(&rectangle)`
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println!("Rectangle perimeter: {}", rectangle.perimeter());
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println!("Rectangle area: {}", rectangle.area());
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let mut square = Rectangle {
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p1: Point::origin(),
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p2: Point::new(1.0, 1.0),
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};
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// Error! `rectangle` is immutable, but this method requires a mutable
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// object.
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//rectangle.translate(1.0, 0.0);
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// TODO ^ Try uncommenting this line
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// Okay! Mutable objects can call mutable methods
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square.translate(1.0, 1.0);
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let pair = Pair(Box::new(1), Box::new(2));
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pair.destroy();
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// Error! Previous `destroy` call "consumed" `pair`
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//pair.destroy();
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// TODO ^ Try uncommenting this line
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}</code></pre></pre>
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<h2 id="exercises"><a class="header" href="#exercises">Exercises</a></h2>
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<h3 id="method"><a class="header" href="#method">Method</a></h3>
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<ol>
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<li>🌟🌟 Methods are similar to functions: Declare with <code>fn</code>, have parameters and a return value. Unlike functions, methods are defined within the context of a struct (or an enum or a trait object), and their first parameter is always <code>self</code>, which represents the instance of the struct the method is being called on.</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">struct Rectangle {
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width: u32,
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height: u32,
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}
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impl Rectangle {
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// Complete the area method which return the area of a Rectangle.
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fn area
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}
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fn main() {
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let rect1 = Rectangle { width: 30, height: 50 };
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assert_eq!(rect1.area(), 1500);
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println!("Success!");
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}</code></pre></pre>
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<ol start="2">
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<li>🌟🌟 <code>self</code> will take the ownership of current struct instance, however, <code>&self</code> will only borrow a reference from the instance.</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">// Only fill in the blanks, DON'T remove any line!
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#[derive(Debug)]
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struct TrafficLight {
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color: String,
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}
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impl TrafficLight {
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pub fn show_state(__) {
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println!("the current state is {}", __.color);
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}
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}
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fn main() {
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let light = TrafficLight{
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color: "red".to_owned(),
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};
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// Don't take the ownership of `light` here.
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light.show_state();
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// ... Otherwise, there will be an error below
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println!("{:?}", light);
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}</code></pre></pre>
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<ol start="3">
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<li>🌟🌟 The <code>&self</code> is actually short for <code>self: &Self</code>. Within an <code>impl</code> block, the type <code>Self</code> is an alias for the type that the <code>impl</code> block is for. Methods must have a parameter named <code>self</code> of type <code>Self</code> for their first parameter, so Rust lets you abbreviate this with only the name <code>self</code> in the first parameter spot.</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">struct TrafficLight {
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color: String,
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}
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impl TrafficLight {
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// Using `Self` to fill in the blank.
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pub fn show_state(__) {
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println!("the current state is {}", self.color);
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}
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// Fill in the blank, DON'T use any variants of `Self`.
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pub fn change_state(__) {
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self.color = "green".to_string()
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}
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}
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fn main() {
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println!("Success!");
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}</code></pre></pre>
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<h3 id="associated-functions"><a class="header" href="#associated-functions">Associated functions</a></h3>
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<ol start="4">
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<li>🌟🌟 All functions defined within an <code>impl</code> block are called associated functions because they’re associated with the type named after the <code>impl</code>. We can define associated functions that don’t have <code>self</code> as their first parameter (and thus are not methods) because they don’t need an instance of the type to work with.</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">#[derive(Debug)]
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struct TrafficLight {
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color: String,
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}
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impl TrafficLight {
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// 1. Implement an associated function `new`,
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// 2. It will return a TrafficLight contains color "red"
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// 3. Must use `Self`, DONT use `TrafficLight` in fn signatures or body
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pub fn new()
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pub fn get_state(&self) -> &str {
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&self.color
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}
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}
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fn main() {
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let light = TrafficLight::new();
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assert_eq!(light.get_state(), "red");
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println!("Success!");
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}</code></pre></pre>
|
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<h3 id="multiple-impl-blocks"><a class="header" href="#multiple-impl-blocks">Multiple <code>impl</code> blocks</a></h3>
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<ol start="5">
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<li>🌟 Each struct is allowed to have multiple impl blocks.</li>
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</ol>
|
||
<pre><pre class="playground"><code class="language-rust editable edition2021">
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struct Rectangle {
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width: u32,
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height: u32,
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||
}
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|
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// Using multiple `impl` blocks to rewrite the code below.
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impl Rectangle {
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fn area(&self) -> u32 {
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self.width * self.height
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||
}
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||
|
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fn can_hold(&self, other: &Rectangle) -> bool {
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self.width > other.width && self.height > other.height
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}
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}
|
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|
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|
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fn main() {
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println!("Success!");
|
||
}</code></pre></pre>
|
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<h3 id="enums"><a class="header" href="#enums">Enums</a></h3>
|
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<ol start="6">
|
||
<li>🌟🌟🌟 We can also implement methods for enums.</li>
|
||
</ol>
|
||
<pre><pre class="playground"><code class="language-rust editable edition2021">
|
||
#[derive(Debug)]
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enum TrafficLightColor {
|
||
Red,
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Yellow,
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Green,
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||
}
|
||
|
||
// Implement TrafficLightColor with a method.
|
||
impl TrafficLightColor {
|
||
|
||
}
|
||
|
||
fn main() {
|
||
let c = TrafficLightColor::Yellow;
|
||
|
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assert_eq!(c.color(), "yellow");
|
||
|
||
println!("{:?}",c);
|
||
}</code></pre></pre>
|
||
<h2 id="practice"><a class="header" href="#practice">Practice</a></h2>
|
||
<p>@todo</p>
|
||
<blockquote>
|
||
<p>You can find the solutions <a href="https://github.com/sunface/rust-by-practice">here</a>(under the solutions path), but only use it when you need it</p>
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</blockquote>
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