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399 lines
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<main>
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<h1 id="reference-and-borrowing"><a class="header" href="#reference-and-borrowing">Reference and Borrowing</a></h1>
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<h3 id="reference"><a class="header" href="#reference">Reference</a></h3>
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<ol>
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<li>🌟</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">
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fn main() {
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let x = 5;
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// Fill the blank
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let p = __;
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println!("the memory address of x is {:p}", p); // One possible output: 0x16fa3ac84
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}</code></pre></pre>
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<ol start="2">
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<li>🌟</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">
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fn main() {
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let x = 5;
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let y = &x;
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// Modify this line only
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assert_eq!(5, y);
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println!("Success!");
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}</code></pre></pre>
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<ol start="3">
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<li>🌟</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">
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// Fix error
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fn main() {
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let mut s = String::from("hello, ");
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borrow_object(s);
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println!("Success!");
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}
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fn borrow_object(s: &String) {}</code></pre></pre>
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<ol start="4">
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<li>🌟</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">
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// Fix error
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fn main() {
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let mut s = String::from("hello, ");
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push_str(s);
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println!("Success!");
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}
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fn push_str(s: &mut String) {
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s.push_str("world")
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}</code></pre></pre>
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<ol start="5">
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<li>🌟🌟</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">
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fn main() {
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let mut s = String::from("hello, ");
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// Fill the blank to make it work
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let p = __;
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p.push_str("world");
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println!("Success!");
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}</code></pre></pre>
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<h4 id="ref"><a class="header" href="#ref">Ref</a></h4>
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<p><code>ref</code> can be used to take references to a value, similar to <code>&</code>.</p>
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<ol start="6">
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<li>🌟🌟🌟</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">
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fn main() {
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let c = '中';
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let r1 = &c;
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// Fill the blank，dont change other code
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let __ r2 = c;
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assert_eq!(*r1, *r2);
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// Check the equality of the two address strings
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assert_eq!(get_addr(r1),get_addr(r2));
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println!("Success!");
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}
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// Get memory address string
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fn get_addr(r: &char) -> String {
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format!("{:p}", r)
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}</code></pre></pre>
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<h3 id="borrowing-rules"><a class="header" href="#borrowing-rules">Borrowing rules</a></h3>
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<ol start="7">
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<li>🌟</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">
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// Remove something to make it work
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// Don't remove a whole line !
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fn main() {
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let mut s = String::from("hello");
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let r1 = &mut s;
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let r2 = &mut s;
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println!("{}, {}", r1, r2);
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println!("Success!");
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}</code></pre></pre>
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<h4 id="mutability"><a class="header" href="#mutability">Mutability</a></h4>
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<ol start="8">
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<li>🌟 Error: Borrow an immutable object as mutable</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">
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fn main() {
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// Fix error by modifying this line
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let s = String::from("hello, ");
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borrow_object(&mut s);
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println!("Success!");
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}
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fn borrow_object(s: &mut String) {}</code></pre></pre>
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<ol start="9">
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<li>🌟🌟 Ok: Borrow a mutable object as immutable</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">
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// This code has no errors!
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fn main() {
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let mut s = String::from("hello, ");
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borrow_object(&s);
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s.push_str("world");
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println!("Success!");
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}
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fn borrow_object(s: &String) {}</code></pre></pre>
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<h3 id="nll"><a class="header" href="#nll">NLL</a></h3>
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<ol start="10">
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<li>🌟🌟</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">
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// Comment one line to make it work
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fn main() {
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let mut s = String::from("hello, ");
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let r1 = &mut s;
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r1.push_str("world");
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let r2 = &mut s;
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r2.push_str("!");
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println!("{}",r1);
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}</code></pre></pre>
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<ol start="11">
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<li>🌟🌟</li>
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</ol>
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<pre><pre class="playground"><code class="language-rust editable edition2021">
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fn main() {
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let mut s = String::from("hello, ");
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let r1 = &mut s;
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let r2 = &mut s;
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// Add one line below to make a compiler error: cannot borrow `s` as mutable more than once at a time
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// You can't use r1 and r2 at the same time
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}</code></pre></pre>
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<blockquote>
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<p>You can find the solutions <a href="https://github.com/sunface/rust-by-practice/blob/master/solutions/ownership/borrowing.md">here</a>(under the solutions path), but only use it when you need it</p>
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</blockquote>
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