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#[derive(Debug, PartialEq, Copy, Clone)]
enum ShirtColor {
    Red,
    Blue,
}

struct Inventory {
    shirts: Vec<ShirtColor>,
}

impl Inventory {
    fn giveaway(&self, user_preference: Option<ShirtColor>) -> ShirtColor {
      // || self.most_stocked() 是闭包表达式
        user_preference.unwrap_or_else(|| self.most_stocked())
    }

    fn most_stocked(&self) -> ShirtColor {
        let mut num_red = 0;
        let mut num_blue = 0;

        for color in &self.shirts {
            match color {
                ShirtColor::Red => num_red += 1,
                ShirtColor::Blue => num_blue += 1,
            }
        }
        if num_red > num_blue {
            ShirtColor::Red
        } else {
            ShirtColor::Blue
        }
    }
}

fn main() {
    let store = Inventory {
        shirts: vec![ShirtColor::Blue, ShirtColor::Red, ShirtColor::Blue],
    };

    let user_pref1 = Some(ShirtColor::Red);
    let giveaway1 = store.giveaway(user_pref1);
    println!(
        "The user with preference {:?} gets {:?}",
        user_pref1, giveaway1
    );

    let user_pref2 = None;
    let giveaway2 = store.giveaway(user_pref2);
    println!(
        "The user with preference {:?} gets {:?}",
        user_pref2, giveaway2
    );
}

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 let expensive_closure = |num: u32| -> u32 {
        println!("calculating slowly...");
        thread::sleep(Duration::from_secs(2));
        num
  };

// 函数
fn  add_one_v1   (x: u32) -> u32 { x + 1 }
// 闭包
let add_one_v2 = |x: u32| -> u32 { x + 1 };
// 省略类型注解
let add_one_v3 = |x|             { x + 1 };
// 省略可选的大括号
let add_one_v4 = |x|               x + 1  ;

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fn main() {
    let list = vec![1, 2, 3];
    println!("Before defining closure: {:?}", list);

    let only_borrows = || println!("From closure: {:?}", list);

    println!("Before calling closure: {:?}", list);
    only_borrows();
    println!("After calling closure: {:?}", list);
}

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fn main() {
    let mut list = vec![1, 2, 3];
    println!("Before defining closure: {:?}", list);

    let mut borrows_mutably = || list.push(7);

    borrows_mutably();
    println!("After calling closure: {:?}", list);
}

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use std::thread;

fn main() {
    let list = vec![1, 2, 3];
    println!("Before defining closure: {:?}", list);

  // 依赖的变量 移动所有权
    thread::spawn(move || println!("From thread: {:?}", list))
        .join()
        .unwrap();
}

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impl<T> Option<T> {
    pub fn unwrap_or_else<F>(self, f: F) -> T
    where
        F: FnOnce() -> T // F 必须要实现 FnOnce Trait
    {
        match self {
            Some(x) => x,
            None => f(),
        }
    }
}

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let v1 = vec![1,2,3];
let v1_iter = v1.iter();
for val in v1_iter {
    println!("Got: {}", val);
}

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pub trait Iterator {
    type Item;

    fn next(&mut self) -> Option<Self::Item>;

    // 此处省略了方法的默认实现
}

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    #[test]
    fn iterator_sum() {
        let v1 = vec![1, 2, 3];

        let v1_iter = v1.iter();

        let total: i32 = v1_iter.sum();

        assert_eq!(total, 6);
    }

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let v1: Vec<i32> = vec![1, 2, 3];
// map 是迭代适配器，为了防止 x 获取所有权但是没 做任何事情，使用collect 做收集
let v2: Vec<_> = v1.iter().map(|x| x + 1).collect();
assert_eq!(v2, vec![2, 3, 4]);