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<h1 id="match-if-let"><a class="header" href="#match-if-let">Match, if let</a></h1>
<h3 id="match"><a class="header" href="#match">Match</a></h3>
<ol>
<li>🌟🌟</li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
// Fill the blanks
enum Direction {
East,
West,
North,
South,
}
fn main() {
let dire = Direction::South;
match dire {
Direction::East =&gt; println!("East"),
__ =&gt; { // Matching South or North here
println!("South or North");
},
_ =&gt; println!(__),
};
}</code></pre></pre>
<ol start="2">
<li>🌟🌟 Match is an expression, so we can use it in assignments.</li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
fn main() {
let boolean = true;
// Fill the blank with a match expression:
//
// boolean = true =&gt; binary = 1
// boolean = false =&gt; binary = 0
let binary = __;
assert_eq!(binary, 1);
println!("Success!");
}</code></pre></pre>
<ol start="3">
<li>🌟🌟 Using match to get the data an enum variant holds.</li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
// Fill in the blanks
enum Message {
Quit,
Move { x: i32, y: i32 },
Write(String),
ChangeColor(i32, i32, i32),
}
fn main() {
let msgs = [
Message::Quit,
Message::Move{x:1, y:3},
Message::ChangeColor(255,255,0)
];
for msg in msgs {
show_message(msg)
}
println!("Success!");
}
fn show_message(msg: Message) {
match msg {
__ =&gt; { // match Message::Move
assert_eq!(a, 1);
assert_eq!(b, 3);
},
Message::ChangeColor(_, g, b) =&gt; {
assert_eq!(g, __);
assert_eq!(b, __);
}
__ =&gt; println!("no data in these variants")
}
}</code></pre></pre>
<h3 id="matches"><a class="header" href="#matches">matches!</a></h3>
<p><a href="https://doc.rust-lang.org/stable/core/macro.matches.html"><code>matches!</code></a> looks like <code>match</code>, but can do something different.</p>
<ol start="4">
<li>🌟🌟</li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
fn main() {
let alphabets = ['a', 'E', 'Z', '0', 'x', '9' , 'Y'];
// Fill the blank with `matches!` to make the code work
for ab in alphabets {
assert!(__)
}
println!("Success!");
} </code></pre></pre>
<ol start="5">
<li>🌟🌟</li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
enum MyEnum {
Foo,
Bar
}
fn main() {
let mut count = 0;
let v = vec![MyEnum::Foo,MyEnum::Bar,MyEnum::Foo];
for e in v {
if e == MyEnum::Foo { // Fix the error by changing only this line
count += 1;
}
}
assert_eq!(count, 2);
println!("Success!");
}</code></pre></pre>
<h3 id="if-let"><a class="header" href="#if-let">If let</a></h3>
<p>For some cases, when matching enums, <code>match</code> is too heavy. We can use <code>if let</code> instead.</p>
<ol start="6">
<li>🌟</li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
fn main() {
let o = Some(7);
// Remove the whole `match` block, using `if let` instead
match o {
Some(i) =&gt; {
println!("This is a really long string and `{:?}`", i);
println!("Success!");
}
_ =&gt; {}
};
}</code></pre></pre>
<ol start="7">
<li>🌟🌟</li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
// Fill in the blank
enum Foo {
Bar(u8)
}
fn main() {
let a = Foo::Bar(1);
__ {
println!("foobar holds the value: {}", i);
println!("Success!");
}
}</code></pre></pre>
<ol start="8">
<li>🌟🌟</li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
enum Foo {
Bar,
Baz,
Qux(u32)
}
fn main() {
let a = Foo::Qux(10);
// Remove the codes below, using `match` instead
if let Foo::Bar = a {
println!("match foo::bar")
} else if let Foo::Baz = a {
println!("match foo::baz")
} else {
println!("match others")
}
}</code></pre></pre>
<h3 id="shadowing"><a class="header" href="#shadowing">Shadowing</a></h3>
<ol start="9">
<li>🌟🌟</li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
// Fix the errors in-place
fn main() {
let age = Some(30);
if let Some(age) = age { // Create a new variable with the same name as previous `age`
assert_eq!(age, Some(30));
} // The new variable `age` goes out of scope here
match age {
// Match can also introduce a new shadowed variable
Some(age) =&gt; println!("age is a new variable, it's value is {}",age),
_ =&gt; ()
}
}</code></pre></pre>
<blockquote>
<p>You can find the solutions <a href="https://github.com/sunface/rust-by-practice/blob/master/solutions/pattern-match/match.md">here</a>(under the solutions path), but only use it when you need it</p>
</blockquote>
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<h1 class="menu-title">Rust By Practice</h1>
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<h1 id="patterns"><a class="header" href="#patterns">Patterns</a></h1>
<ol>
<li>🌟🌟 Use <code>|</code> to match several values, use <code>..=</code> to match an inclusive range.</li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
fn main() {}
fn match_number(n: i32) {
match n {
// Match a single value
1 =&gt; println!("One!"),
// Fill in the blank with `|`, DON'T use `..` or `..=`
__ =&gt; println!("match 2 -&gt; 5"),
// Match an inclusive range
6..=10 =&gt; {
println!("match 6 -&gt; 10")
},
_ =&gt; {
println!("match -infinite -&gt; 0 or 11 -&gt; +infinite")
}
}
}</code></pre></pre>
<ol start="2">
<li>🌟🌟🌟 The <code>@</code> operator lets us create a variable that holds a value, at the same time we are testing that value to see whether it matches a pattern.</li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
struct Point {
x: i32,
y: i32,
}
fn main() {
// Fill in the blank to let p match the second arm
let p = Point { x: __, y: __ };
match p {
Point { x, y: 0 } =&gt; println!("On the x axis at {}", x),
// Second arm
Point { x: 0..=5, y: y@ (10 | 20 | 30) } =&gt; println!("On the y axis at {}", y),
Point { x, y } =&gt; println!("On neither axis: ({}, {})", x, y),
}
}</code></pre></pre>
<ol start="3">
<li>🌟🌟🌟</li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
// Fix the errors
enum Message {
Hello { id: i32 },
}
fn main() {
let msg = Message::Hello { id: 5 };
match msg {
Message::Hello {
id: 3..=7,
} =&gt; println!("Found an id in range [3, 7]: {}", id),
Message::Hello { id: newid@10 | 11 | 12 } =&gt; {
println!("Found an id in another range [10, 12]: {}", newid)
}
Message::Hello { id } =&gt; println!("Found some other id: {}", id),
}
}</code></pre></pre>
<ol start="4">
<li>🌟🌟 A match guard is an additional if condition specified after the pattern in a match arm that must also match, along with the pattern matching, for that arm to be chosen.</li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
// Fill in the blank to make the code work, `split` MUST be used
fn main() {
let num = Some(4);
let split = 5;
match num {
Some(x) __ =&gt; assert!(x &lt; split),
Some(x) =&gt; assert!(x &gt;= split),
None =&gt; (),
}
println!("Success!");
}</code></pre></pre>
<ol start="5">
<li>🌟🌟 Ignoring remaining parts of the value with <code>..</code></li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
// Fill the blank to make the code work
fn main() {
let numbers = (2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048);
match numbers {
__ =&gt; {
assert_eq!(first, 2);
assert_eq!(last, 2048);
}
}
println!("Success!");
}</code></pre></pre>
<ol start="6">
<li>🌟🌟 Using pattern <code>&amp;mut V</code> to match a mutable reference requires you to be very careful, due to <code>V</code> being a value after matching.</li>
</ol>
<pre><pre class="playground"><code class="language-rust editable edition2021">
// FIX the error with least changing
// DON'T remove any code line
fn main() {
let mut v = String::from("hello,");
let r = &amp;mut v;
match r {
&amp;mut value =&gt; value.push_str(" world!")
}
}</code></pre></pre>
<blockquote>
<p>You can find the solutions <a href="https://github.com/sunface/rust-by-practice/blob/master/solutions/pattern-match/patterns.md">here</a>(under the solutions path), but only use it when you need it</p>
</blockquote>
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