Rustのパターンとは，型の構造に一致する記法
match式や他の構文と組み合わせることで，プログラムをコントロールできる
match
この章では改めてRustのパターンとは何かを説明する
match VALUE { PATTERN => EXPRESSION, PATTERN => EXPRESSION, PATTERN => EXPRESSION, }
if let
if let Some(color) = favorite_color { ... } else if let Ok(age) = age { ... }
while let
let mut stack = Vec::new(); stack.push(1); stack.push(2); stack.push(3); while let Some(top) = stack.pop() { println!("{}", top); }
for
let v = vec!['a', 'b', 'c']; for (index, value) in v.iter().enumerate() { println!("{} is at index {}", value, index); } // a is at index 0 // b is at index 1 // c is at index 2
let (x, y, z) = (1, 2, 3);
fn print_coordinates(&(x, y): &(i32, i32)) { ... }
let x = 5;
if let Some(x) = a_value
None
some_option_value
let Some(x) = some_option_value;
error[E0005]: refutable pattern in local binding: `None` not covered (エラー: ローカル束縛に論駁可能なパターン: `None`がカバーされていません) --> | 3 | let Some(x) = some_option_value; | ^^^^^^^ pattern `None` not covered
x
5
if let x = 5 { println!("{}", x); };
error[E0162]: irrefutable if-let pattern (エラー: 論駁不可能なif-letパターン) --> <anon>:2:8 | 2 | if let x = 5 { | ^ irrefutable pattern
match x { 1 => println!("one"), // 1 2 => println!("two"), // 2 3 => println!("three"), // 3 _ => println!("anything"), // なんでも }
fn main() { let x = Some(5); let y = 10; match x { // 50だったよ Some(50) => println!("Got 50"), // マッチしたよ Some(y) => println!("Matched, y = {:?}", y), // 既定のケース _ => println!("Default case, x = {:?}", x), } // 最後にはx = {}, y = {} println!("at the end: x = {:?}, y = {:?}", x, y); }
|
let x = 1; match x { // 1か2 1 | 2 => println!("one or two"), // 3 3 => println!("three"), // なんでも _ => println!("anything"), }
..=
char
let x = 5; match x { // 1から5まで 1 ..= 5 => println!("one through five"), // それ以外 _ => println!("something else"), }
Eq
==
let x = 'c'; match x { // ASCII文字前半 'a' ... 'j' => println!("early ASCII letter"), // ASCII文字後半 'k' ... 'z' => println!("late ASCII letter"), // それ以外 _ => println!("something else"), }
分解
分配
destructing to break apart
destructing
struct Point { x: i32, y: i32, } fn main() { let p = Point { x: 0, y: 7 }; let Point { x: a, y: b } = p; // let Point { a, b } = p; でもOK // let Point { y: b, x: a } = p; でもOK assert_eq!(0, a); assert_eq!(7, b); }
enum Message { Quit, Coordinate(i32, i32), } fn main() { let msg = Message::Coordinate(10, 5); match msg { Message::Quit => { println!("The Quit variant has no data to destructure.") }, Message::Coordinate(x, y) => { println!("Change the coordinate to x {} and y {}", x, y) } } }
let points = vec![ Point { x: 0, y: 0 }, Point { x: 1, y: 5 }, Point { x: 10, y: -3 }, ]; let sum_of_squares: i32 = points .iter() .map(|&Point { x, y }| x * x + y * y) .sum();
let ((feet, inches), Point {x, y}) = ((3, 10), Point { x: 3, y: -10 });
_
..
fn foo(_: i32, y: i32) { // このコードは、y引数を使うだけです: {} println!("This code only uses the y parameter: {}", y); // "This code only uses the y parameter: 4"と表示される } fn main() { foo(3, 4); }
let mut setting_value = Some(5); let new_setting_value = Some(10); match (setting_value, new_setting_value) { (Some(_), Some(_)) => { // 既存の値の変更を上書きできません println!("Can't overwrite an existing customized value"); } _ => { setting_value = new_setting_value; } }
let numbers = (2, 4, 8, 16, 32); match numbers { (first, _, third, _, fifth) => { // 何らかの数値: {}, {}, {} println!("Some numbers: {}, {}, {}", first, third, fifth) }, }
fn main() { let _x = 5; let y = 10; }
for _ in 0..10 { do_something(); }
(0..10).for_each(|_| do_something());
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), }
let numbers = (2, 4, 8, 16, 32); match numbers { (.., second, ..) => { println!("Some numbers: {}", second) }, }
error: `..` can only be used once per tuple or tuple struct pattern (エラー: `..`は、タプルやタプル構造体パターン1つにつき、1回しか使用できません) --> src/main.rs:5:22 | 5 | (.., second, ..) => { | ^^
ref
mut ref
let robot_name = Some(String::from("Bors")); match robot_name { Some(ref name) => println!("Found a name: {}", name), None => (), } println!("robot_name is: {:?}", robot_name);
if
let num = Some(4); match num { // 5未満です: {} Some(x) if x < 5 => println!("less than five: {}", x), Some(x) => println!("{}", x), None => (), }
enum Message { Hello { id: i32 }, } let msg = Message::Hello { id: 5 }; match msg { Message::Hello { id: id_variable @ 3...7 } => { // 範囲内のidが見つかりました: {} println!("Found an id in range: {}", id_variable) }, Message::Hello { id: 10...12 } => { // 別の範囲内のidが見つかりました println!("Found an id in another range") }, Message::Hello { id } => { // それ以外のidが見つかりました println!("Found some other id: {}", id) }, }