Rust中的Impls & Traits

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✅impls经常被用来定义Rust的structs和enums方法
✅ Traits有点儿像OOP语言中的interfaces。它们通常被用来定义必须被提供的功能性。大部分的traits可以为单一类型实现

但是traits也可以包含默认方法实现,在实现类型的时候默认方法可以被重写

1、Impl without traits

struct Player {
    first_name: String,
    last_name: String,
}

impl Player {
    fn full_name(&self) -> String {
        format!("{} {}", self.first_name, self.last_name)
    }
}

fn main() {
    let player_1 = Player {
        first_name: "Rafael".to_string(),
        last_name: "Nadal".to_string(),
    };

    println!("Player 01: {}", player_1.full_name());
}

// ⭐️ Implementation must appear in the same crate as the self type

// 💡 And also in Rust, new traits can be implemented for existing types even for types like i8, f64 and etc.
// Same way existing traits can be implemented for new types you are creating.
// But we can not implement existing traits into existing types.

Impls & traits,without default methods

struct Player {
    first_name: String,
    last_name: String,
}

trait FullName {
    fn full_name(&self) -> String;
}

impl FullName for Player {
    fn full_name(&self) -> String {
        format!("{} {}", self.first_name, self.last_name)
    }
}

fn main() {
    let player_2 = Player {
        first_name: "Roger".to_string(),
        last_name: "Federer".to_string(),
    };

    println!("Player 02: {}", player_2.full_name());
}

// 🔎 Other than functions, traits can contain constants and types.

2、Impls, traits & default methods

trait Foo {
    fn bar(&self);
    fn baz(&self) { println!("We called baz."); }
}

正如你所看到的方法的第一个参数是特殊的,类型是itself。要么是self,&self要么是 &mut self; self如果它是栈上的值,&self如果它是一个参考,&mut self如果它是一个可变的参考
Impls with Associated functions
一些其他的语言支持静态方法。在这种情况下,我们可以直接通过class调用一个函数而不是创建一个对象。在Rust中,我们把它们称为关联函数。我们在从struct中调用他们的时候使用::而不是.
例如:
Person::new("Elon Musk Jr");

struct Player {
    first_name: String,
    last_name: String,
}

impl Player {
    fn new(first_name: String, last_name: String) -> Player {
        Player {
            first_name : first_name,
            last_name : last_name,
        }
    }

    fn full_name(&self) -> String {
        format!("{} {}", self.first_name, self.last_name)
    }
}

fn main() {
    let player_name = Player::new("Serena".to_string(), "Williams".to_string()).full_name();
    println!("Player: {}", player_name);
}

// We have used :: notation for `new()` and . notation for `full_name()`

// 🔎 Also in here, instead of using new() and full_name() separately as two expressions, 
// we can use Method Chaining. ex. `player.add_points(2).get_point_count();`

3、Traits with generics

trait From<T> {
    fn from(T) -> Self;
}
    impl From<u8> for u16 {
        //...
    }
    impl From<u8> for u32{
        //...
    }
    
// Should specify after the trait name like generic functions

4、Traits inheritance

trait Person {
    fn full_name(&self) -> String;
}

    trait Employee : Person { // Employee inherits from person trait
      fn job_title(&self) -> String;
    }

    trait ExpatEmployee : Employee + Expat { // ExpatEmployee inherits from Employee and Expat traits
      fn additional_tax(&self) -> f64;
    }

5、Trait objects
🔍当Rust支持静态的发送的时候,它通过一个叫trait objects的方法也支持动态的发送

trait GetSound {
    fn get_sound(&self) -> String;
}

struct Cat {
    sound: String,
}
    impl GetSound for Cat {
        fn get_sound(&self) -> String {
            self.sound.clone()
        }
    }

struct Bell {
    sound: String,
}
    impl GetSound for Bell {
        fn get_sound(&self) -> String {
            self.sound.clone()
        }
    }


fn make_sound<T: GetSound>(t: &T) {
    println!("{}!", t.get_sound())
}

fn main() {
    let kitty = Cat { sound: "Meow".to_string() };
    let the_bell = Bell { sound: "Ding Dong".to_string() };

    make_sound(&kitty); // Meow!
    make_sound(&the_bell); // Ding Dong!
}

注:有些特定指示我并没有翻译,但也很简单,可以理解是什么意思

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