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add traits.md
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sunface
@ -1,7 +1,417 @@
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1.
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```rust
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trait Hello {
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fn say_hi(&self) -> String {
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String::from("hi")
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}
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fn say_something(&self) -> String;
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}
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struct Student {}
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impl Hello for Student {
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fn say_something(&self) -> String {
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String::from("I'm a good student")
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}
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}
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struct Teacher {}
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impl Hello for Teacher {
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fn say_hi(&self) -> String {
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String::from("Hi, I'm your new teacher")
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}
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fn say_something(&self) -> String {
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String::from("I'm not a bad teacher")
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}
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}
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fn main() {
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let s = Student {};
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assert_eq!(s.say_hi(), "hi");
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assert_eq!(s.say_something(), "I'm a good student");
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let t = Teacher {};
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assert_eq!(t.say_hi(), "Hi, I'm your new teacher");
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assert_eq!(t.say_something(), "I'm not a bad teacher");
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}
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```
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1.
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2.
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```rust
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// `Centimeters`, a tuple struct that can be compared
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#[derive(PartialEq, PartialOrd)]
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struct Centimeters(f64);
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// `Inches`, a tuple struct that can be printed
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#[derive(Debug)]
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struct Inches(i32);
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impl Inches {
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fn to_centimeters(&self) -> Centimeters {
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let &Inches(inches) = self;
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Centimeters(inches as f64 * 2.54)
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}
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}
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// Add some attributes to make the code work
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// DON'T modify other codes
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#[derive(Debug,PartialEq,PartialOrd)]
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struct Seconds(i32);
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fn main() {
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let _one_second = Seconds(1);
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println!("One second looks like: {:?}", _one_second);
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let _this_is_true = (_one_second == _one_second);
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let _this_is_true = (_one_second > _one_second);
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let foot = Inches(12);
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println!("One foot equals {:?}", foot);
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let meter = Centimeters(100.0);
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let cmp =
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if foot.to_centimeters() < meter {
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"smaller"
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} else {
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"bigger"
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};
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println!("One foot is {} than one meter.", cmp);
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}
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```
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3.
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```rust
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use std::ops;
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// implement fn multiply to make the code work
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// As mentiond above, `+` needs `T` to implement `std::ops::Add` Trait
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// so, what about `*` ? You can find the answer here: https://doc.rust-lang.org/core/ops/
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fn multiply<T: ops::Mul<Output = T>>(x: T, y: T) -> T {
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x * y
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}
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fn main() {
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assert_eq!(6, multiply(2u8, 3u8));
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assert_eq!(5.0, multiply(1.0, 5.0));
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}
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```
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4.
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```rust
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use std::ops;
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struct Foo;
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struct Bar;
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#[derive(PartialEq, Debug)]
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struct FooBar;
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#[derive(PartialEq, Debug)]
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struct BarFoo;
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// The `std::ops::Add` trait is used to specify the functionality of `+`.
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// Here, we make `Add<Bar>` - the trait for addition with a RHS of type `Bar`.
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// The following block implements the operation: Foo + Bar = FooBar
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impl ops::Add<Bar> for Foo {
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type Output = FooBar;
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fn add(self, _rhs: Bar) -> FooBar {
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FooBar
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}
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}
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impl ops::Sub<Bar> for Foo {
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type Output = BarFoo;
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fn sub(self, _rhs: Bar) -> BarFoo {
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BarFoo
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}
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}
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fn main() {
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// DON'T modify the below code
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// you need to derive some trait for FooBar to make it comparable
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assert_eq!(Foo + Bar, FooBar);
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assert_eq!(Foo - Bar, BarFoo);
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}
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```
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5.
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```rust
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// implement `fn summary` to make the code work
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// fix the errors without removing any code line
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trait Summary {
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fn summarize(&self) -> String;
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}
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#[derive(Debug)]
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struct Post {
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title: String,
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author: String,
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content: String,
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}
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impl Summary for Post {
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fn summarize(&self) -> String {
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format!("The author of post {} is {}", self.title, self.author)
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}
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}
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#[derive(Debug)]
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struct Weibo {
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username: String,
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content: String,
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}
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impl Summary for Weibo {
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fn summarize(&self) -> String {
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format!("{} published a weibo {}", self.username, self.content)
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}
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}
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fn main() {
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let post = Post {
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title: "Popular Rust".to_string(),
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author: "Sunface".to_string(),
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content: "Rust is awesome!".to_string(),
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};
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let weibo = Weibo {
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username: "sunface".to_string(),
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content: "Weibo seems to be worse than Tweet".to_string(),
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};
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summary(&post);
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summary(&weibo);
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println!("{:?}", post);
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println!("{:?}", weibo);
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}
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fn summary(t: &impl Summary) {
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let _ = t.summarize();
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}
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```
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6.
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```rust
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struct Sheep {}
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struct Cow {}
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trait Animal {
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fn noise(&self) -> String;
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}
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impl Animal for Sheep {
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fn noise(&self) -> String {
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"baaaaah!".to_string()
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}
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}
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impl Animal for Cow {
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fn noise(&self) -> String {
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"moooooo!".to_string()
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}
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}
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// Returns some struct that implements Animal, but we don't know which one at compile time.
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// FIX the erros here, you can make a fake random, or you can use trait object
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fn random_animal(random_number: f64) -> impl Animal {
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if random_number < 0.5 {
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Sheep {}
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} else {
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Sheep {}
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}
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}
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fn main() {
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let random_number = 0.234;
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let animal = random_animal(random_number);
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println!("You've randomly chosen an animal, and it says {}", animal.noise());
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}
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```
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```rust
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struct Sheep {}
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struct Cow {}
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trait Animal {
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fn noise(&self) -> String;
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}
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impl Animal for Sheep {
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fn noise(&self) -> String {
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"baaaaah!".to_string()
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}
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}
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impl Animal for Cow {
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fn noise(&self) -> String {
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"moooooo!".to_string()
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}
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}
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// Returns some struct that implements Animal, but we don't know which one at compile time.
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// FIX the erros here, you can make a fake random, or you can use trait object
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fn random_animal(random_number: f64) -> Box<dyn Animal> {
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if random_number < 0.5 {
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Box::new(Sheep {})
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} else {
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Box::new(Cow{})
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}
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}
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fn main() {
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let random_number = 0.234;
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let animal = random_animal(random_number);
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println!("You've randomly chosen an animal, and it says {}", animal.noise());
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}
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```
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7.
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```rust
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fn main() {
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assert_eq!(sum(1, 2), 3);
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assert_eq!(sum(1.0, 2.0), 3.0);
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}
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fn sum<T: std::ops::Add<Output = T>>(x: T, y: T) -> T {
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x + y
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}
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```
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```rust
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fn main() {
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assert_eq!(sum(1, 2), 3);
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assert_eq!(sum(1.0, 2.0), 3.0);
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}
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fn sum<T>(x: T, y: T) -> T
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where
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T: std::ops::Add<Output = T>,
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{
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x + y
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}
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```
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8.
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```rust
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struct Pair<T> {
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x: T,
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y: T,
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}
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impl<T> Pair<T> {
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fn new(x: T, y: T) -> Self {
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Self {
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x,
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y,
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}
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}
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}
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impl<T: std::fmt::Debug + PartialOrd> Pair<T> {
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fn cmp_display(&self) {
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if self.x >= self.y {
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println!("The largest member is x = {:?}", self.x);
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} else {
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println!("The largest member is y = {:?}", self.y);
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}
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}
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}
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#[derive(Debug, PartialEq, PartialOrd)]
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struct Unit(i32);
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fn main() {
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let pair = Pair{
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x: Unit(1),
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y: Unit(3)
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};
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pair.cmp_display();
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}
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```
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9.
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```rust
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fn example1() {
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// `T: Trait` is the commonly used way
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// `T: Fn(u32) -> u32` specifies that we can only pass a closure to `T`
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struct Cacher<T: Fn(u32) -> u32> {
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calculation: T,
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value: Option<u32>,
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}
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impl<T: Fn(u32) -> u32> Cacher<T> {
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fn new(calculation: T) -> Cacher<T> {
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Cacher {
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calculation,
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value: None,
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}
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}
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fn value(&mut self, arg: u32) -> u32 {
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match self.value {
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Some(v) => v,
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None => {
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let v = (self.calculation)(arg);
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self.value = Some(v);
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v
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},
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}
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}
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}
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let mut cacher = Cacher::new(|x| x+1);
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assert_eq!(cacher.value(10), 11);
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assert_eq!(cacher.value(15), 11);
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}
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fn example2() {
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// We can also use `where` to constrain `T`
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struct Cacher<T>
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where T: Fn(u32) -> u32,
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{
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calculation: T,
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value: Option<u32>,
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}
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impl<T> Cacher<T>
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where T: Fn(u32) -> u32,
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{
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fn new(calculation: T) -> Cacher<T> {
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Cacher {
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calculation,
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value: None,
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}
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}
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fn value(&mut self, arg: u32) -> u32 {
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match self.value {
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Some(v) => v,
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None => {
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let v = (self.calculation)(arg);
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self.value = Some(v);
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v
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},
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}
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}
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}
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let mut cacher = Cacher::new(|x| x+1);
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assert_eq!(cacher.value(20), 21);
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assert_eq!(cacher.value(25), 21);
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}
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fn main() {
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example1();
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example2();
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}
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```
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