Differences

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--- rust [2024/07/11 20:09] – [Control flow] utedass
+++ rust [2024/07/11 20:46] (current) – [Matching] utedass
@@ Line 72: / Line 72: @@
         println!("the value is: {element}");
     }
+</code>
+==== References and Borrowing ====
+<code rust>
+let mut x: Box<i32> = Box::new(1);
+let a: i32 = *x;         // *x reads the heap value, so a = 1
+*x += 1;                 // *x on the left-side modifies the heap value,
+                         //     so x points to the value 2
+let r1: &Box<i32> = &x;  // r1 points to x on the stack
+let b: i32 = **r1;       // two dereferences get us to the heap value
+let r2: &i32 = &*x;      // r2 points to the heap value directly
+let c: i32 = *r2;    // so only one dereference is needed to read it
+// Mutable reference
+let mut v: Vec<i32> = vec![1, 2, 3];
+let num: &mut i32 = &mut v[2];
+*num += 1;
 </code>
 ==== Struct methods ====
@@ Line 152: / Line 171: @@
     dbg!(&rect1);
 }
+</code>
+==== Enums ====
+<code rust>
+enum IpAddrKind {
+    V4,
+    V6,
+}
+fn main() {
+    let four = IpAddrKind::V4;
+    let six: IpAddrKind = IpAddrKind::V6; // Explicit type
+}
+</code>
+Enums can have different content for their different enumerations.
+<code rust>
+enum Message {
+    Quit,
+    Move { x: i32, y: i32 },
+    Write(String),
+    ChangeColor(i32, i32, i32),
+}
+</code>
+They can also have functions
+<code rust>
+    enum Message {
+        Quit,
+        Move { x: i32, y: i32 },
+        Write(String),
+        ChangeColor(i32, i32, i32),
+    }
+    impl Message {
+        fn call(&self) {
+            // method body would be defined here
+        }
+    }
+    let m = Message::Write(String::from("hello"));
+    m.call();
+</code>
+There is the special Option type available in the standard library std::option::Option
+<code rust>
+enum Option<T> {
+    None,
+    Some(T),
+}
+</code>
+<code rust>
+let some_number = Some(5);
+let some_char = Some('e');
+let absent_number: Option<i32> = None;
+</code>
+==== Matching ====
+<code rust>
+enum UsState {
+    Alabama,
+    Alaska,
+    // --snip--
+}
+enum Coin {
+    Penny,
+    Nickel,
+    Dime,
+    Quarter(UsState),
+}
+fn value_in_cents(coin: Coin) -> u8 {
+    match coin {
+        Coin::Penny => 1,
+        Coin::Nickel => 5,
+        Coin::Dime => 10,
+        Coin::Quarter(state) => {
+            println!("State quarter from {:?}!", state);
+        }
+    }
+}
+</code>
+Can match integers as well
+<code rust>
+    let dice_roll = 9;
+    match dice_roll {
+=> add_fancy_hat(),
+=> remove_fancy_hat(),
+        other => move_player(other),
+    }
+    fn add_fancy_hat() {}
+    fn remove_fancy_hat() {}
+    fn move_player(num_spaces: u8) {}
 </code>