commit
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@ -1,10 +1,10 @@
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# match, if let
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# Match, if let
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### match
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### Match
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1. ππ
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```rust,editable
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// fill the blanks
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// Fill the blanks
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enum Direction {
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East,
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West,
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@ -16,7 +16,7 @@ fn main() {
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let dire = Direction::South;
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match dire {
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Direction::East => println!("East"),
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__ => { // matching South or North here
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__ => { // Matching South or North here
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println!("South or North");
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},
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_ => println!(__),
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@ -24,13 +24,13 @@ fn main() {
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}
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```
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2. ππ match is an expression, so we can use it in assignments
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2. ππ Match is an expression, so we can use it in assignments.
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```rust,editable
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fn main() {
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let boolean = true;
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// fill the blank with an match expression:
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// Fill the blank with a match expression:
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//
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// boolean = true => binary = 1
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// boolean = false => binary = 0
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@ -38,14 +38,14 @@ fn main() {
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assert_eq!(binary, 1);
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println!("Success!")
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println!("Success!");
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}
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```
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3. ππ using match to get the data an enum variant holds
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3. ππ Using match to get the data an enum variant holds.
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```rust,editable
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// fill in the blanks
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// Fill in the blanks
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enum Message {
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Quit,
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Move { x: i32, y: i32 },
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@ -64,7 +64,7 @@ fn main() {
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show_message(msg)
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}
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println!("Success!")
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println!("Success!");
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}
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fn show_message(msg: Message) {
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@ -83,7 +83,7 @@ fn show_message(msg: Message) {
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```
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### matches!
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[`matches!`](https://doc.rust-lang.org/stable/core/macro.matches.html) looks like `match`, but can do something different
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[`matches!`](https://doc.rust-lang.org/stable/core/macro.matches.html) looks like `match`, but can do something different.
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4. ππ
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```rust,editable
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@ -91,12 +91,12 @@ fn show_message(msg: Message) {
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fn main() {
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let alphabets = ['a', 'E', 'Z', '0', 'x', '9' , 'Y'];
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// fill the blank with `matches!` to make the code work
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// Fill the blank with `matches!` to make the code work
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for ab in alphabets {
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assert!(__)
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}
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println!("Success!")
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println!("Success!");
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}
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```
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@ -113,19 +113,19 @@ fn main() {
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let v = vec![MyEnum::Foo,MyEnum::Bar,MyEnum::Foo];
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for e in v {
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if e == MyEnum::Foo { // fix the error with changing only this line
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if e == MyEnum::Foo { // Fix the error by changing only this line
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count += 1;
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}
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}
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assert_eq!(count, 2);
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println!("Success!")
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println!("Success!");
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}
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```
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### if let
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For some cases, when matching enums, `match` is too heavy, we can use `if let` instead.
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### If let
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For some cases, when matching enums, `match` is too heavy. We can use `if let` instead.
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6. π
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```rust,editable
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@ -133,12 +133,12 @@ For some cases, when matching enums, `match` is too heavy, we can use `if let` i
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fn main() {
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let o = Some(7);
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// remove the whole `match` block, using `if let` instead
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// Remove the whole `match` block, using `if let` instead
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match o {
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Some(i) => {
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println!("This is a really long string and `{:?}`", i);
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println!("Success!")
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println!("Success!");
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}
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_ => {}
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};
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@ -148,7 +148,7 @@ fn main() {
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7. ππ
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```rust,editable
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// fill in the blank
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// Fill in the blank
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enum Foo {
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Bar(u8)
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}
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@ -159,7 +159,7 @@ fn main() {
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__ {
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println!("foobar holds the value: {}", i);
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println!("Success!")
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println!("Success!");
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}
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}
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```
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@ -176,7 +176,7 @@ enum Foo {
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fn main() {
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let a = Foo::Qux(10);
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// remove the codes below, using `match` instead
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// Remove the codes below, using `match` instead
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if let Foo::Bar = a {
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println!("match foo::bar")
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} else if let Foo::Baz = a {
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9. ππ
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```rust,editable
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// fix the errors in-place
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// Fix the errors in-place
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fn main() {
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let age = Some(30);
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if let Some(age) = age { // create a new variable with the same name as previous `age`
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if let Some(age) = age { // Create a new variable with the same name as previous `age`
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assert_eq!(age, Some(30));
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} // the new variable `age` goes out of scope here
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} // The new variable `age` goes out of scope here
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match age {
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// match can also introduce a new shadowed variable
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// Match can also introduce a new shadowed variable
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Some(age) => println!("age is a new variable, it's value is {}",age),
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_ => ()
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}
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@ -1,16 +1,16 @@
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# Patterns
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1. ππ use `|` to match several values, use `..=` to match a inclusive range
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1. ππ Use `|` to match several values, use `..=` to match an inclusive range.
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```rust,editable
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fn main() {}
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fn match_number(n: i32) {
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match n {
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// match a single value
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// Match a single value
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1 => println!("One!"),
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// fill in the blank with `|`, DON'T use `..` ofr `..=`
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// Fill in the blank with `|`, DON'T use `..` or `..=`
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__ => println!("match 2 -> 5"),
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// match an inclusive range
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// Match an inclusive range
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6..=10 => {
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println!("match 6 -> 10")
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},
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}
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```
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2. πππ The `@` 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.
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2. πππ The `@` 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.
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```rust,editable
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struct Point {
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}
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fn main() {
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// fill in the blank to let p match the second arm
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// Fill in the blank to let p match the second arm
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let p = Point { x: __, y: __ };
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match p {
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Point { x, y: 0 } => println!("On the x axis at {}", x),
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// second arm
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// Second arm
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Point { x: 0..=5, y: y@ (10 | 20 | 30) } => println!("On the y axis at {}", y),
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Point { x, y } => println!("On neither axis: ({}, {})", x, y),
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}
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```rust,editable
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// fix the errors
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// Fix the errors
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enum Message {
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Hello { id: i32 },
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}
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4. ππ 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.
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```rust,editable
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// fill in the blank to make the code work, `split` MUST be used
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// Fill in the blank to make the code work, `split` MUST be used
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fn main() {
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let num = Some(4);
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let split = 5;
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None => (),
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}
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println!("Success!")
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println!("Success!");
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}
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```
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5. ππ Ignoring remaining parts of the value with `..`
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```rust,editable
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// fill the blank to make the code work
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// Fill the blank to make the code work
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fn main() {
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let numbers = (2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048);
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}
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}
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println!("Success!")
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println!("Success!");
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}
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```
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6. ππ Using pattern `&mut V` to match a mutable reference needs you to be very careful due to `V` being a value after matching
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6. ππ Using pattern `&mut V` to match a mutable reference needs you to be very careful, due to `V` being a value after matching.
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```rust,editable
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// FIX the error with least changing
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Loadingβ¦
Reference in New Issue