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6.6 KiB
6.6 KiB
id | title |
---|---|
8c351588-1dc2-4955-86b5-a13181367cf9 | Rust Pattern Syntax |
Examples
Matching Literals
fn main() {
let x = 1;
match x {
1 => println!("one"),
2 => println!("two"),
3 => println!("three"),
_ => println!("anything"),
}
}
Matching Named Variables
fn main() {
let x = Some(5);
let y = 10;
match x {
Some(50) => println!("Got 50"),
Some(y) => println!("Matched, y = {:?}", y),
_ => println!("Default case, x = {:?}", x),
}
println!("at the end: x = {:?}, y = {:?}", x, y);
}
Multiple Patterns
fn main() {
let x = 1;
match x {
1 | 2 => println!("one or two"),
3 => println!("three"),
_ => println!("anything"),
}
}
Matching Ranges of Values with ..=
fn main() {
let x = 5;
match x {
1..=5 => println!("one through five"),
_ => println!("something else"),
}
}
fn main() {
let x = 'c';
match x {
'a'..='j' => println!("early ASCII letter"),
'k'..='z' => println!("late ASCII letter"),
_ => println!("something else"),
}
}
Destructuring
Destructuring to break apart Values
-
Destructuring Structs
struct Point { x: i32, y: i32, } fn main() { let p = Point { x: 0, y: 7 }; let Point { x: a, y: b } = p; assert_eq!(0, a); assert_eq!(7, b); }
-
Shorthand version
struct Point { x: i32, y: i32, } fn main() { let p = Point { x: 0, y: 7 }; let Point { x, y } = p; assert_eq!(0, x); assert_eq!(7, y); }
#+RESULTS:
-
Destructuring and matching literal values in one pattern
struct Point {
x: i32,
y: i32,
}
fn main() {
let p = Point { x: 0, y: 7 };
match p {
Point { x, y: 0 } => println!("On the x axis at {}", x),
Point { x: 0, y } => println!("On the y axis at {}", y),
Point { x, y } => println!("On neither axis: ({}, {})", x, y),
}
}
Destructuring Enums
Enums can also be deconstructed:
enum Message {
Quit,
Move { x: i32, y: i32 },
Write(String),
ChangeColor(i32, i32, i32),
}
fn main() {
let msg = Message::ChangeColor(0, 160, 255);
match msg {
Message::Quit => println!("The Quit variant has no data to destructure."),
Message::Move { x, y } => {
println!("Move in the x direction {} and in the y direction {}", x, y);
}
Message::Write(text) => println!("Text message: {}", text),
Message::ChangeColor(r, g, b) => {
println!("Change the color to red {}, green {}, and blue {}", r, g, b)
}
}
}
Destructuring nested Structs and Enums
Nested structs and enums can also be destructured:
enum Color {
Rgb(i32, i32, i32),
Hsv(i32, i32, i32),
}
enum Message {
Quit,
Move { x: i32, y: i32 },
Write(String),
ChangeColor(Color),
}
fn main() {
let msg = Message::ChangeColor(Color::Hsv(0, 160, 255));
match msg {
Message::ChangeColor(Color::Rgb(r, g, b)) => {
println!("Change the color to red {}, green {}, and blue {}", r, g, b)
}
Message::ChangeColor(Color::Hsv(h, s, v)) => println!(
"Change the color to hue {}, saturation {}, and value {}",
h, s, v
),
_ => (),
}
}
Destructuring Structs and Tuples
fn main() {
struct Point {
x: i32,
y: i32,
}
let ((feet, inches), Point { x, y }) = ((3, 10), Point { x: 3, y: -10 });
}
Ignoring Values in a Pattern
_
-
Ignoring an entire Value with _
fn foo(_: i32, y: i32) { println!("This code only uses the y parameter: {}", y); } fn main() { foo(3, 4); }
-
Ignoring parts of a Value with a nested _
fn main() { let mut setting_value = Some(5); let new_setting_value = Some(10); match (setting_value, new_setting_value) { (Some(_), Some(_)) => { println!("Can't overwrite an existing customized value"); } _ => { setting_value = new_setting_value; } } println!("setting is {:?}", setting_value); }
fn main() { let numbers = (2, 4, 8, 16, 32); match numbers { (first, _, third, _, fifth) => println!("Some numbers: {}, {}, {}", first, third, fifth), } }
-
Ignoring an unused Variable by starting its name with _
fn main() { let _x = 5; }
#+RESULTS:
…
-
Ignoring remaining parts of a Value with …
fn main() { struct Point { x: i32, y: i32, z: i32, } let origin = Point { x: 0, y: 0, z: 0 }; match origin { Point { x, .. } => println!("x is {}", x), } }
fn main() { let numbers = (2, 4, 8, 16, 32); match numbers { (first, .., last) => { println!("Some numbers: {}, {}", first, last); } } }
Extra conditionals with Match Guards
fn main() {
let num = Some(4);
match num {
Some(x) if x < 5 => println!("less than five: {}", x),
Some(x) => println!("{}", x),
None => (),
}
}
fn main() {
let x = Some(5);
let y = 10;
match x {
Some(50) => println!("Got 50"),
Some(n) if n == y => println!("Matched, n = {}", n),
_ => println!("Default case, x = {:?}", x),
}
println!("at the end: x = {:?}, y = {}", x, y);
}
fn main() {
let x = 4;
let y = false;
match x {
4 | 5 | 6 if y => println!("yes"),
_ => println!("no"),
}
}
@ Bindings
fn main() {
enum Message {
Hello { id: i32 },
}
let msg = Message::Hello { id: 5 };
match msg {
Message::Hello {
id: id_variable @ 3..=7,
} => println!("Found an id in range: {}", id_variable),
Message::Hello { id: 10..=12 } => println!("Found an id in another range"),
Message::Hello { id } => println!("Found some other id: {}", id),
}
}