Rust学习笔记
Rust编程语言入门教程课程笔记
参考教材: The Rust Programming Language (by Steve Klabnik and Carol Nichols, with contributions from the Rust Community)
Lecture 18: Patterns and Matching
src/main.rs
fn main() {//match arms// match VALUE {// PATTERN => EXPRESSION,// PATTERN => EXPRESSION,// PATTERN => EXPRESSION,// _ => EXPRESSION,// }let x = 1;match x {1 => println!("one"),2 => println!("two"),3 => println!("three"),_ => println!("anything"),}//if let//else if//else if letlet favorite_color: Option<&str> = None;let is_tuesday = false;let age: Result<u8, _> = "34".parse();if let Some(color) = favorite_color {println!("Using your favorite color, {color}, as the background");} else if is_tuesday {println!("Tuesday is green day!");} else if let Ok(age) = age {//use the shadowed age variableif age > 30 {println!("Using purple as the background color");} else {println!("Using orange as the background color");}} else {println!("Using blue as the background color");} //while letlet mut stack = Vec::new();stack.push(1);stack.push(2);stack.push(3);while let Some(top) = stack.pop(){println!("{}", top);}//for loopslet v = vec!['a', 'b', 'c'];for (index, value) in v.iter().enumerate(){println!("{} is at index {}", value, index);}//let statements//let Pattern = Expression;let (x, y, z) = (1, 2, 3);//function parametersfoo(3);let point = (3, 5);print_coordinates(&point);//Refutability: Whether a Pattern Might Fail to Matchlet some_option_value: Option<i32> = None;// let Some(x) = some_option_value; //error: refutable pattern in local binding: `None` not coveredif let Some(x) = some_option_value {println!("{}", x);}//Pattern Syntax//Matching Named Variableslet 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);//x = Some(5), y = 10//Multiple Patternslet x = 1;match x {1 | 2 => println!("one or two"),3 => println!("three"),_ => println!("anything"),}//Matching Ranges of Values with ...let x = 5;match x {1..=5 => println!("one through five"),_ => println!("something else"),}let x = 'c';match x {'a'..='j' => println!("early ASCII letter"),'k'..='z' => println!("late ASCII letter"),_ => println!("something else"),}//Destructuring to Break Apart Valueslet p = Point { x: 0, y: 7 };let Point { x: a, y: b } = p; //let Point { x, y } = p;assert_eq!(0, a);assert_eq!(7, b);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 Enumslet 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 {x} and in the y direction {y}");}Message::Write(text) => {println!("Text message: {text}");}Message::ChangeColor(r, g, b) => {println!("Change the color to red {r}, green {g}, and blue {b}",)}}//Destructuring Nested Structs and Enumslet msg = Message3::ChangeColor(Color::Hsv(0, 160, 255));match msg {Message3::ChangeColor(Color::Rgb(r, g, b)) => {println!("Change color to red {r}, green {g}, and blue {b}");}Message3::ChangeColor(Color::Hsv(h, s, v)) => {println!("Change color to hue {h}, saturation {s}, value {v}")}_ => (),}//Destructuring Structs and Tupleslet ((feet, inches), Point { x, y }) = ((3, 10), Point { x: 3, y: -10 });//Ignoring Values in a Patternfoo2(3, 4);//Ignoring Parts of a Value with a Nested _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);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 _let _x = 5;let y = 10;println!("{}", y);let s = Some(String::from("Hello!"));//if let Some(_s) = s {// println!("found a string");//}//println!("{:?}", s);if let Some(_) = s {println!("found a string");}println!("{:?}", s);//Ignoring Remaining Parts of a Value with ..let origin = Point2 { x: 0, y: 0, z: 0 };match origin {Point2 { x, .. } => println!("x is {}", x),}let numbers = (2, 4, 8, 16, 32);match numbers {(first, .., last) => {println!("Some numbers: {first}, {last}");}}//match numbers {// (.., second, ..) => { //error: It’s impossible for Rust to determine how many values in the tuple to ignore before matching a value with second and then how many further values to ignore thereafter.// println!("Some numbers: {}", second)// },// }//Extra Conditionals with Match Guardslet num = Some(4);match num {Some(x) if x % 2 == 0 => println!("The number {} is even", x),Some(x) => println!("The number {} is odd", x),None => (),}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 = {y}", x);let x = 4;let y = false;match x {4 | 5 | 6 if y => println!("yes"),_ => println!("no"),}// @ Bindingsenum Message2 {Hello { id: i32 },}let msg = Message2::Hello { id: 5 };match msg {Message2::Hello {id: id_variable @ 3..=7,} => println!("Found an id in range: {id_variable}"),Message2::Hello { id: 10..=12 } => {println!("Found an id in another range")}Message2::Hello { id } => println!("Found some other id: {id}"),}
}struct Point {x: i32,y: i32,
}struct Point2 {x: i32,y: i32,z: i32,
}enum Message {Quit,Move { x: i32, y: i32 },Write(String),ChangeColor(i32, i32, i32),
}enum Message3 {Quit,Move { x: i32, y: i32 },Write(String),ChangeColor(Color),
}enum Color {Rgb(i32, i32, i32),Hsv(i32, i32, i32),
}fn foo(x: i32) {// code goes here
}fn foo2(_: i32, y: i32) {println!("This code only uses the y parameter: {}", y);
}fn print_coordinates(&(x, y): &(i32, i32)) {println!("Current location: ({}, {})", x, y);
}
)
)
)
