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fn main() {
    let x = 5;
    // 填写空白处
    // let p = __;
    let p = &x;

    println!("x 的内存地址是 {:p}", p); // output: 0x16fa3ac84 具体值不一定
}

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fn main() {
    let x = 5;
    let y = &x;

    // 只能修改以下行
    // assert_eq!(5, y);
    assert_eq!(5, *y);
}

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// 修复错误
fn main() {
    let mut s = String::from("hello, ");

    // borrow_object(s)
    borrow_object(&s)
}

fn borrow_object(s: &String) {}

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// 修复错误
fn main() {
    let mut s = String::from("hello, ");

    // push_str(s)
    push_str(&mut s)
}

fn push_str(s: &mut String) {
    s.push_str("world")
}

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fn main() {
    let mut s = String::from("hello, ");

    // 填写空白处，让代码工作
    // let p = __;
    let p = &mut s;

    p.push_str("world");
    println!("{p}");//hello, world
    println!("{s}");//hello, world
}

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fn main() {
    let c = '中';

    let r1 = &c;
    // 填写空白处，但是不要修改其它行的代码
    // let __ r2 = c;
    let ref r2 = c;

    assert_eq!(*r1, *r2);
    
    // 判断两个内存地址的字符串是否相等
    assert_eq!(get_addr(r1),get_addr(r2));
}

// 获取传入引用的内存地址的字符串形式
fn get_addr(r: &char) -> String {
    format!("{:p}", r)
}

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// 移除代码某个部分，让它工作
// 你不能移除整行的代码！
fn main() {
    let mut s = String::from("hello");

    // let r1 = &mut s;
    let r1 = &s;
    // let r2 = &mut s;
    let r2 = &s;

    println!("{}, {}", r1, r2);
}

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fn main() {
    // 通过修改下面一行代码来修复错误
    // let s = String::from("hello, ");
    let mut s = String::from("hello, ");

    borrow_object(&mut s)
}

fn borrow_object(s: &mut String) {}

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// 下面的代码没有任何错误
fn main() {
    let mut s = String::from("hello, ");

    borrow_object(&s);
    
    s.push_str("world");
}

fn borrow_object(s: &String) {}

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// 注释掉一行代码让它工作
fn main() {
    let mut s = String::from("hello, ");

    let r1 = &mut s;
    r1.push_str("world");
    let r2 = &mut s;
    r2.push_str("!");
    
    // println!("{}",r1);
}

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fn main() {
    let mut s = String::from("hello, ");

    let r1 = &mut s;
    let r2 = &mut s;

    // 在下面增加一行代码, 人为制造编译错误：cannot borrow `s` as mutable more than once at a time
    // 你不能同时使用 r1 和 r2
    println!("{}", r1);
}