add patterns.md

src/pattern-match/patterns.md

@@ -1,6 +1,6 @@
 # Patterns
 
-🌟🌟 Using `|` to match several values.
+🌟🌟 use `|` to match several values, use `..=` to match a inclusive range
 ```rust,editable
 
 fn main() {}
@@ -21,3 +21,78 @@ fn match_number(n: i32) {
 }
 ```
 
+🌟🌟🌟 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.
+```rust,editable
+
+struct Point {
+    x: i32,
+    y: i32,
+}
+
+fn main() {
+    // fill in the blank to let p match the second arm
+    let p = Point { x: __, y: __ };
+
+    match p {
+        Point { x, y: 0 } => println!("On the x axis at {}", x),
+        // second arm
+        Point { x: 0..=5, y: y@ (10 | 20 | 30) } => println!("On the y axis at {}", y),
+        Point { x, y } => println!("On neither axis: ({}, {})", x, y),
+    }
+}
+```
+
+🌟🌟🌟
+
+```rust,editable
+
+// fix the errors
+enum Message {
+    Hello { id: i32 },
+}
+
+fn main() {
+    let msg = Message::Hello { id: 5 };
+
+    match msg {
+        Message::Hello {
+            id:  3..=7,
+        } => println!("Found an id in range [3, 7]: {}", id),
+        Message::Hello { id: newid@10 | 11 | 12 } => {
+            println!("Found an id in another range [10, 12]: {}", newid)
+        }
+        Message::Hello { id } => println!("Found some other id: {}", id),
+    }
+}
+```
+
+🌟🌟 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.
+```rust,editable
+
+// fill in the blank to make the code work, `split` MUST be used
+fn main() {
+    let num = Some(4);
+    let split = 5;
+    match num {
+        Some(x) __ => assert!(x < split),
+        Some(x) => assert!(x >= split),
+        None => (),
+    }
+}
+```
+
+🌟🌟 Ignoring remaining parts of the value with `..`
+```rust,editable
+
+// fill the blank to make the code work
+fn main() {
+    let numbers = (2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048);
+
+    match numbers {
+        __ => {
+           assert_eq!(first, 2);
+           assert_eq!(last, 2048);
+        }
+    }
+}
+```