add match excercise

data/1.rust初阶/2.rust基本概念/9.表达式/config.json

@@ -2,5 +2,7 @@
   "node_id": "rust-73665fa29a214d2bb55ead28656063cb",
   "keywords": [],
   "children": [],
-  "export": []
+  "export": [
+      "match.json"
+  ]
 }
\ No newline at end of file

data/1.rust初阶/2.rust基本概念/9.表达式/match.json

+{
+    "type": "code_options",
+    "author": "jacky_rust",
+    "source": "match.md",
+    "notebook_enable": false
+}
\ No newline at end of file

data/1.rust初阶/2.rust基本概念/9.表达式/match.md

+# match 表达式
+
+Rust 的 match 表达式类似 C 语言的 switch 语句，但比之更强大。
+
+```rust
+fn main() {
+    let x = 42;
+
+    match x {
+        0      => { println!("zero"); }
+        1      => { println!("one"); }
+        2      => { println!("two"); }
+        3..=41 => { println!("between 3 and 41 (ends included)"); }
+        42     => { println!("The answer"); }
+        n @ 43..=99
+               => { println!("Hint: the answer is smaller than {}", n); } 
+        _      => { println!("out of the range"); }
+    }
+}
+```
+
+match 还可以直接使用多值模式匹配  
+
+```rust
+fn main() {
+    let p = (2, 4);
+
+    match p {
+        (0, 0)    => { println!("Bingo! Origin of coordinates."); }
+        (0, _y)   => { println!("On the X axis."); }
+        (_x, 0)   => { println!("On the Y axis."); }
+        _         => { println!("Not on the axises"); }
+    }
+}
+```
+
+match 还可以将返回值作为右值给变量赋值。另外要注意 match 的每个分支返回的数据类型要相同。
+
+下列选项中，能正确打印一个不在 X 或 Y 轴上的点的 x, y 坐标的是: 
+
+## 答案
+
+```rust
+fn main() {
+    let p = (2, 4);
+
+    let result = match p {
+        (0, 0)    => { (0, 0) }
+        (0, _y)   => { (0, 0) }
+        (_x, 0)   => { (0, 0) }
+        (x, y)    => { (x, y) }
+    };
+
+    println!("x: {}, y: {}", result.0, result.1);
+}
+```
+
+## 选项
+
+### let 赋值语句不要忘记分号
+
+```rust
+fn main() {
+    let p = (2, 4);
+
+    let result = match p {
+        (0, 0)    => { (0, 0) }
+        (0, _y)   => { (0, 0) }
+        (_x, 0)   => { (0, 0) }
+        (x, y)    => { (x, y) }
+    }
+
+    println!("x: {}, y: {}", result.0, result.1);
+}
+```
+
+### match 分支要返回同类似的值
+
+```rust
+fn main() {
+    let p = (2, 4);
+
+    let result = match p {
+        (0, 0)    => { println!("Bingo! Origin of coordinates."); }
+        (0, _y)   => { println!("On the X axis."); }
+        (_x, 0)   => { println!("On the Y axis."); }
+        (x, y)    => { (x, y) }
+    };
+
+    println!("x: {}, y: {}", x, y);
+}
+```
+
+### match 分支要用逗号分隔，或用花括号包括语句以自动返回 () 值
+
+```rust
+fn main() {
+    let p = (2, 4);
+
+    match p {
+        (0, 0)    => println!("Bingo! Origin of coordinates.");
+        (0, _y)   => println!("On the X axis.");
+        (_x, 0)   => println!("On the Y axis.");
+        (x, y)    => println!("x: {}, y: {}", x, y);
+    }
+}
+```