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<ol class="chapter"><li class="chapter-item expanded "><a href="Chapter_0.html"><strong aria-hidden="true">1.</strong> Update</a></li><li class="chapter-item expanded "><a href="Chapter_1.html"><strong aria-hidden="true">2.</strong> Introduction</a></li><li class="chapter-item expanded "><a href="Chapter_2.html"><strong aria-hidden="true">3.</strong> Who am I?</a></li><li class="chapter-item expanded "><a href="Chapter_3.html"><strong aria-hidden="true">4.</strong> Writing Rust in Easy English</a></li><li class="chapter-item expanded "><a href="Chapter_4.html"><strong aria-hidden="true">5.</strong> Rust Playground</a></li><li class="chapter-item expanded "><a href="Chapter_5.html"><strong aria-hidden="true">6.</strong> 🚧 and ⚠️</a></li><li class="chapter-item expanded "><a href="Chapter_6.html"><strong aria-hidden="true">7.</strong> Comments</a></li><li class="chapter-item expanded "><a href="Chapter_7.html"><strong aria-hidden="true">8.</strong> Types</a></li><li class="chapter-item expanded "><a href="Chapter_8.html"><strong aria-hidden="true">9.</strong> Type inference</a></li><li class="chapter-item expanded "><a href="Chapter_9.html"><strong aria-hidden="true">10.</strong> Printing 'hello, world!'</a></li><li class="chapter-item expanded "><a href="Chapter_10.html"><strong aria-hidden="true">11.</strong> Display and debug</a></li><li class="chapter-item expanded "><a href="Chapter_11.html"><strong aria-hidden="true">12.</strong> Mutability (changing)</a></li><li class="chapter-item expanded "><a href="Chapter_12.html"><strong aria-hidden="true">13.</strong> The stack, the heap, and pointers</a></li><li class="chapter-item expanded "><a href="Chapter_13.html"><strong aria-hidden="true">14.</strong> More about printing</a></li><li class="chapter-item expanded "><a href="Chapter_14.html" class="active"><strong aria-hidden="true">15.</strong> Strings</a></li><li class="chapter-item expanded "><a href="Chapter_15.html"><strong aria-hidden="true">16.</strong> const and static</a></li><li class="chapter-item expanded "><a href="Chapter_16.html"><strong aria-hidden="true">17.</strong> More on references</a></li><li class="chapter-item expanded "><a href="Chapter_17.html"><strong aria-hidden="true">18.</strong> Mutable references</a></li><li class="chapter-item expanded "><a href="Chapter_18.html"><strong aria-hidden="true">19.</strong> Giving references to functions</a></li><li class="chapter-item expanded "><a href="Chapter_19.html"><strong aria-hidden="true">20.</strong> Copy types</a></li><li class="chapter-item expanded "><a href="Chapter_20.html"><strong aria-hidden="true">21.</strong> Collection types</a></li><li class="chapter-item expanded "><a href="Chapter_21.html"><strong aria-hidden="true">22.</strong> Vectors</a></li><li class="chapter-item expanded "><a href="Chapter_22.html"><strong aria-hidden="true">23.</strong> Tuples</a></li><li class="chapter-item expanded "><a href="Chapter_23.html"><strong aria-hidden="true">24.</strong> Control flow</a></li><li class="chapter-item expanded "><a href="Chapter_24.html"><strong aria-hidden="true">25.</strong> Structs</a></li><li class="chapter-item expanded "><a href="Chapter_25.html"><strong aria-hidden="true">26.</strong> Enums</a></li><li class="chapter-item expanded "><a href="Chapter_26.html"><strong aria-hidden="true">27.</strong> Loops</a></li><li class="chapter-item expanded "><a href="Chapter_27.html"><strong aria-hidden="true">28.</strong> Implementing structs and enums</a></li><li class="chapter-item expanded "><a href="Chapter_28.html"><strong aria-hidden="true">29.</strong> Destructuring</a></li><li class="chapter-item expanded "><a href="Chapter_29.html"><strong aria-hidden="true">30.</strong> References and the dot operator</a></li><li class="chapter-item expanded "><a href="Chapter_30.html"><strong aria-hidden="true">31.</strong> Generics</a></li><li class="chapter-item expanded "><a href="Chapter_31.html"><strong aria-hidden="true">32.</strong> Option and Result</a></li><li class="chapter-item expanded "><a href="Chapter_32.html"><strong aria-hidden="true">33.</strong> Other collections</a></li><li class="chapter-item expanded "><a href="Chapter_33.html"><strong aria-hidden="true">34.</strong> The ? operator</a></li><li class="chapter-item expanded "><a href="Chapter_34.html"><strong aria-hidden="true">35.</strong> Traits</a></li><li class="chapter-item expanded "><a href="Chapter_35.html"><strong aria-hidden="true">36.</strong> Chaining methods</a></li><li class="chapter-item expanded "><a href="Chapter_36.html"><strong aria-hidden="true">37.</strong> Iterators</a></li><li class="chapter-item expanded "><a href="Chapter_37.html"><strong aria-hidden="true">38.</strong> Closures</a></li><li class="chapter-item expanded "><a href="Chapter_38.html"><strong aria-hidden="true">39.</strong> The dbg! macro and .inspect</a></li><li class="chapter-item expanded "><a href="Chapter_39.html"><strong aria-hidden="true">40.</strong> Types of &str</a></li><li class="chapter-item expanded "><a href="Chapter_40.html"><strong aria-hidden="true">41.</strong> Lifetimes</a></li><li class="chapter-item expanded "><a href="Chapter_41.html"><strong aria-hidden="true">42.</strong> Interior mutability</a></li><li class="chapter-item expanded "><a href="Chapter_42.html"><strong aria-hidden="true">43.</strong> Cow</a></li><li class="chapter-item expanded "><a href="Chapter_43.html"><strong aria-hidden="true">44.</strong> Type aliases</a></li><li class="chapter-item expanded "><a href="Chapter_44.html"><strong aria-hidden="true">45.</strong> The todo! macro</a></li><li class="chapter-item expanded "><a href="Chapter_45.html"><strong aria-hidden="true">46.</strong> Rc</a></li><li class="chapter-item expanded "><a href="Chapter_46.html"><strong aria-hidden="true">47.</strong> Multiple threads</a></li><li class="chapter-item expanded "><a href="Chapter_47.html"><strong aria-hidden="true">48.</strong> Closures in functions</a></li><li class="chapter-item expanded "><a href="Chapter_48.html"><strong aria-hidden="true">49.</strong> impl Trait</a></li><li class="chapter-item expanded "><a href="Chapter_49.html"><strong aria-hidden="true">50.</strong> Arc</a></li><li class="chapter-item expanded "><a href="Chapter_50.html"><strong aria-hidden="true">51.</strong> Channels</a></li><li class="chapter-item expanded "><a href="Chapter_51.html"><strong aria-hidden="true">52.</strong> Reading Rust documentation</a></li><li class="chapter-item expanded "><a href="Chapter_52.html"><strong aria-hidden="true">53.</strong> Attributes</a></li><li class="chapter-item expanded "><a href="Chapter_53.html"><strong aria-hidden="true">54.</strong> Box</a></li><li class="chapter-item expanded "><a href="Chapter_54.html"><strong aria-hidden="true">55.</strong> Box around traits</a></li><li class="chapter-item expanded "><a href="Chapter_55.html"><strong aria-hidden="true">56.</strong> Default and the builder pattern</a></li><li class="chapter-item expanded "><a href="Chapter_56.html"><strong aria-hidden="true">57.</strong> Deref and DerefMut</a></li><li class="chapter-item expanded "><a href="Chapter_57.html"><strong aria-hidden="true">58.</strong> Crates and modules</a></li><li class="chapter-item expanded "><a href="Chapter_58.html"><strong aria-hidden="true">59.</strong> Testing</a></li><li class="chapter-item expanded "><a href="Chapter_59.html"><strong aria-hidden="true">60.</strong> External crates</a></li><li class="chapter-item expanded "><a href="Chapter_60.html"><strong aria-hidden="true">61.</strong> A tour of the standard library</a></li><li class="chapter-item expanded "><a href="Chapter_61.html"><strong aria-hidden="true">62.</strong> Writing macros</a></li><li class="chapter-item expanded "><a href="Chapter_62.html"><strong aria-hidden="true">63.</strong> cargo</a></li><li class="chapter-item expanded "><a href="Chapter_63.html"><strong aria-hidden="true">64.</strong> Taking user input</a></li><li class="chapter-item expanded "><a href="Chapter_64.html"><strong aria-hidden="true">65.</strong> Using files</a></li><li class="chapter-item expanded "><a href="Chapter_65.html"><strong aria-hidden="true">66.</strong> cargo doc</a></li><li class="chapter-item expanded "><a href="Chapter_66.html"><strong aria-hidden="true">67.</strong> The end?</a></li></ol>
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<h2 id="strings"><a class="header" href="#strings">Strings</a></h2>
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<p><strong><a href="https://youtu.be/pSyaGzGg26o">See this chapter on YouTube</a></strong></p>
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<p>Rust has two main types of strings: <code>String</code> and <code>&str</code>. What is the difference?</p>
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<ul>
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<li><code>&str</code> is a simple string. When you write <code>let my_variable = "Hello, world!"</code>, you create a <code>&str</code>. A <code>&str</code> is very fast.</li>
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<li><code>String</code> is a more complicated string. It is a bit slower, but it has more functions. A <code>String</code> is a pointer, with data on the heap.</li>
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</ul>
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<p>Also note that <code>&str</code> has the <code>&</code> in front of it because you need a reference to use a <code>str</code>. That's because of the reason we saw above: the stack needs to know the size. So we give it a <code>&</code> that it knows the size of, and then it is happy. Also, because you use a <code>&</code> to interact with a <code>str</code>, you don't own it. But a <code>String</code> is an <em>owned</em> type. We will soon learn why that is important to know.</p>
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<p>Both <code>&str</code> and <code>String</code> are UTF-8. For example, you can write:</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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let name = "서태지"; // This is a Korean name. No problem, because a &str is UTF-8.
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let other_name = String::from("Adrian Fahrenheit Țepeș"); // Ț and ș are no problem in UTF-8.
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}
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</code></pre></pre>
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<p>You can see in <code>String::from("Adrian Fahrenheit Țepeș")</code> that it is easy to make a <code>String</code> from a <code>&str</code>. The two types are very closely linked together, even though they are different.</p>
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<p>You can even write emojis, thanks to UTF-8.</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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let name = "😂";
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println!("My name is actually {}", name);
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}
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</code></pre></pre>
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<p>On your computer that will print <code>My name is actually 😂</code> unless your command line can't print it. Then it will show <code>My name is actually <20></code>. But Rust has no problem with emojis or any other Unicode.</p>
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<p>Let's look at the reason for using a <code>&</code> for <code>str</code>s again to make sure we understand.</p>
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<ul>
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<li><code>str</code> is a dynamically sized type (dynamically sized = the size can be different). For example, the names "서태지" and "Adrian Fahrenheit Țepeș" are not the same size:</li>
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</ul>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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println!("A String is always {:?} bytes. It is Sized.", std::mem::size_of::<String>()); // std::mem::size_of::<Type>() gives you the size in bytes of a type
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println!("And an i8 is always {:?} bytes. It is Sized.", std::mem::size_of::<i8>());
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println!("And an f64 is always {:?} bytes. It is Sized.", std::mem::size_of::<f64>());
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println!("But a &str? It can be anything. '서태지' is {:?} bytes. It is not Sized.", std::mem::size_of_val("서태지")); // std::mem::size_of_val() gives you the size in bytes of a variable
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println!("And 'Adrian Fahrenheit Țepeș' is {:?} bytes. It is not Sized.", std::mem::size_of_val("Adrian Fahrenheit Țepeș"));
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}
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</code></pre></pre>
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<p>This prints:</p>
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<pre><code class="language-text">A String is always 24 bytes. It is Sized.
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And an i8 is always 1 bytes. It is Sized.
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And an f64 is always 8 bytes. It is Sized.
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But a &str? It can be anything. '서태지' is 9 bytes. It is not Sized.
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And 'Adrian Fahrenheit Țepeș' is 25 bytes. It is not Sized.
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</code></pre>
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<p>That is why we need a &, because <code>&</code> makes a pointer, and Rust knows the size of the pointer. So the pointer goes on the stack. If we wrote <code>str</code>, Rust wouldn't know what to do because it doesn't know the size.</p>
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<p>There are many ways to make a <code>String</code>. Here are some:</p>
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<ul>
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<li><code>String::from("This is the string text");</code> This a method for String that takes text and creates a String.</li>
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<li><code>"This is the string text".to_string()</code>. This is a method for &str that makes it a String.</li>
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<li>The <code>format!</code> macro. This is like <code>println!</code> except it creates a String instead of printing. So you can do this:</li>
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</ul>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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let my_name = "Billybrobby";
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let my_country = "USA";
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let my_home = "Korea";
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let together = format!(
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"I am {} and I come from {} but I live in {}.",
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my_name, my_country, my_home
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);
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}
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</code></pre></pre>
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<p>Now we have a String named <em>together</em>, but did not print it yet.</p>
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<p>One other way to make a String is called <code>.into()</code> but it is a bit different because <code>.into()</code> isn't just for making a <code>String</code>. Some types can easily convert to and from another type using <code>From</code> and <code>.into()</code>. And if you have <code>From</code>, then you also have <code>.into()</code>. <code>From</code> is clearer because you already know the types: you know that <code>String::from("Some str")</code> is a <code>String</code> from a <code>&str</code>. But with <code>.into()</code>, sometimes the compiler doesn't know:</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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let my_string = "Try to make this a String".into(); // ⚠️
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}
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</code></pre></pre>
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<p>Rust doesn't know what type you want, because many types can be made from a <code>&str</code>. It says, "I can make a &str into a lot of things. Which one do you want?"</p>
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<pre><code class="language-text">error[E0282]: type annotations needed
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--> src\main.rs:2:9
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|
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2 | let my_string = "Try to make this a String".into();
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| ^^^^^^^^^ consider giving `my_string` a type
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</code></pre>
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<p>So you can do this:</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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let my_string: String = "Try to make this a String".into();
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}
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</code></pre></pre>
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<p>And now you get a String.</p>
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