Complete options exercises

exercises/12_options/options1.rs

@@ -3,7 +3,6 @@
 // Execute `rustlings hint options1` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
 
 // This function returns how much icecream there is left in the fridge.
 // If it's before 10PM, there's 5 pieces left. At 10PM, someone eats them
@@ -13,7 +12,13 @@ fn maybe_icecream(time_of_day: u16) -> Option<u16> {
     // value of 0 The Option output should gracefully handle cases where
     // time_of_day > 23.
     // TODO: Complete the function body - remember to return an Option!
-    ???
+    if time_of_day > 23 {
+        None
+    } else if time_of_day >= 22 {
+        Some(0)
+    } else {
+        Some(5)
+    }
 }
 
 #[cfg(test)]
@@ -34,6 +39,10 @@ mod tests {
         // TODO: Fix this test. How do you get at the value contained in the
         // Option?
         let icecreams = maybe_icecream(12);
-        assert_eq!(icecreams, 5);
+        assert_eq!(icecreams.unwrap(), 5);
     }
 }
+
+// Option has two variants: None and Some 
+// Some is a tuple struct that wraps a value with type T
+// None indicates failure or lack of value

exercises/12_options/options2.rs

@@ -3,8 +3,6 @@
 // Execute `rustlings hint options2` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
-
 #[cfg(test)]
 mod tests {
     #[test]
@@ -13,16 +11,21 @@ mod tests {
         let optional_target = Some(target);
 
         // TODO: Make this an if let statement whose value is "Some" type
-        word = optional_target {
+        // This block is checking whether or not optional_target is a typen  of Some(T)
+        // Since it is, it's binding the value of Some(target) to word. 
+
+        // The result is word = Some(Some(target))
+        if let Some(word) = optional_target {
             assert_eq!(word, target);
         }
-    }
+    } 
 
     #[test]
     fn layered_option() {
         let range = 10;
         let mut optional_integers: Vec<Option<i8>> = vec![None];
 
+        // Range is inclusive of the start and exclusive of the end. 
         for i in 1..(range + 1) {
             optional_integers.push(Some(i));
         }
@@ -32,7 +35,8 @@ mod tests {
         // TODO: make this a while let statement - remember that vector.pop also
         // adds another layer of Option<T>. You can stack `Option<T>`s into
         // while let and if let.
-        integer = optional_integers.pop() {
+       while let Some(Some(integer)) = optional_integers.pop() {
+            // Removes the last character for the vector and return it
             assert_eq!(integer, cursor);
             cursor -= 1;
         }

exercises/12_options/options3.rs

@@ -3,7 +3,6 @@
 // Execute `rustlings hint options3` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
 
 struct Point {
     x: i32,
@@ -13,8 +12,9 @@ struct Point {
 fn main() {
     let y: Option<Point> = Some(Point { x: 100, y: 200 });
 
-    match y {
+    match y { // &y can also be used here to borrow instead of moving ownership of y to the match expression
-        Some(p) => println!("Co-ordinates are {},{} ", p.x, p.y),
+        // ref is used during pattern matching. 
+        Some(ref p) => println!("Co-ordinates are {},{} ", p.x, p.y),
         _ => panic!("no match!"),
     }
     y; // Fix without deleting this line.