Finish chapter6: Enums and pattern matching

src/main.rs

@@ -618,7 +618,7 @@ fn defining_enum() {
 
         println!("Instead of combining an enum and a struct, we can put the datas directly into the enum: {:?}", home);
         println!("Doing so also permit to have differents types for each elements: {:?}", loopback);
-        println!("NOTE: The standard library implements an IpAddr enum, beter use it than our custom one 😉.");
+        println!("NOTE: The standard library implements an IpAddr enum, better use it than our custom one 😉.");
 
         impl IpAddr {
             fn route(&self)  {
@@ -644,12 +644,121 @@ fn defining_enum() {
         println!("We will have to take care of the `Option` enum, so checking if the value is _y: {:?} `Some` or _z: {:?} `None`.", _y, _z);
         println!("Instead of believing there is a value when really there is a null value.");
     }
+
+    println!();
 }
 
 fn match_control_flow() {
-    unimplemented!()
+    {
+        #[derive(Debug)]
+        enum UsState {
+            _Alabama,
+            Alaska,
+            // ...
         }
 
-fn concise_control_flow_if_let() {
+        enum UsCoin {
-    unimplemented!()
+            Penny,
+            Nickel,
+            Dime,
+            Quarter(UsState),
+        }
+
+        fn value_in_cents(coin: UsCoin) -> u32 {
+            match coin {
+                UsCoin::Penny => {
+                    println!("Lucky penny!");
+                    1
+                },
+                UsCoin::Nickel => 5,
+                UsCoin::Dime => 10,
+                UsCoin::Quarter(state) => {
+                    println!("State quarter from {:?}!", state);
+                    25
+                },
+            }
+        }
+
+        println!("With the match control flow we can get the value of a Penny: {:?}", value_in_cents(UsCoin::Penny));
+        println!("Or any other US coin vakue of the `enum`. Nickel: {:?}", value_in_cents(UsCoin::Nickel));
+        println!("The compiler will make sure we mach every value possibles values when using the `match` control flow. Dime: {:?}", value_in_cents(UsCoin::Dime));
+        println!("It's like a `switch case break` where you have to make sure all options are covered.");
+        println!("We can even match with the value contains in the enum. Quarter: {:?}", value_in_cents(UsCoin::Quarter(UsState::Alaska)));
+    }
+
+    {
+        fn plus_one(x: Option<i32>) -> Option<i32> {
+            match x {
+                None => None,
+                Some(i) => Some(i + 1),
+            }
+        }
+
+        let five = Some(5);
+        let six = plus_one(five);
+        let none = plus_one(None);
+
+        println!("Example use of `match` with the `Option` enum: five = {:?}, plus_one = {:?}, None plus_one = {:?}", five, six, none);
+
+        let some_u8_value = 7u8;
+        match some_u8_value {
+            1 => println!("one"),
+            3 => println!("three"),
+            5 => println!("five"),
+            7 => println!("seven"),
+            _ => (),                    // `_` is a placeholder and `()` is the unit value
+        }
+    }
+
+    println!();
+}
+
+#[allow(dead_code, unused_assignments, unused_variables)]
+fn concise_control_flow_if_let() {
+    println!("When we only want to match one element, a `match` control flow may be berbose.");
+    println!("Instead we can use the `if let [else]` syntax.");
+
+    let some_u8_value = Some(0u8);
+
+    // This is the same as ...
+    match some_u8_value {
+        Some(3) => println!("three"),
+        _ => (),
+    }
+    // ... this.
+    if let Some(3) = some_u8_value {
+        println!("three");
+    }
+
+    #[derive(Clone, Copy, Debug)]
+    enum UsState {
+        Alabama,
+        Alaska,
+        // ...
+    }
+    #[derive(Clone, Copy)]
+    enum UsCoin {
+        Penny,
+        Nickel,
+        Dime,
+        Quarter(UsState),
+    }
+
+    let coin = UsCoin::Penny;
+
+    // And this is the same as ...
+    let mut count = 0;
+    match coin {
+        UsCoin::Quarter(state) => println!("State quarter from {:?}!", state),
+        _ => count += 1,
+    }
+    // ... this.
+    let mut count = 0;
+    if let UsCoin::Quarter(state) = coin {
+        println!("State quarter from {:?}!", state);
+    } else {
+        count += 1;
+    }
+
+    println!();
 }