Improve closures_iterators exercise instructions, change the challenge

exercise/closures_iterators/src/main.rs

@@ -2,15 +2,17 @@
 #[allow(unused_mut)]
 
 fn main() {
-    // 1. Create a closure that returns the square of an integer (the number multiplied by itself),
-    // and assign the closure to a variable called "square".
+    // 1. Uncomment the code below. Create a closure that returns the square of an integer (the
+    // number multiplied by itself), and assign the closure to the "square" variable. Then run the
+    // code and make sure it works.
 
     // let square = ...
-    //println!("5 squared is {}", square(5));
+    // println!("5 squared is {}", square(5));
 
-    // 2. Uncomment the code below.  Finish the .map() by passing it a closure which takes a tuple
-    // of two integers, and returns a tuple with the first integer incremented by 1, and the second
-    // integer left alone.  For example, (0, 1) should become (1, 1).
+    // 2. Uncomment the code below.  Finish the .map() iterator adaptor call by passing it a closure
+    // which takes a tuple of two integers as a parameter, and returns a tuple with the first
+    // integer incremented by 1, and the second integer left alone.  For example, if given the input
+    // (0, 1), it should return (1, 1). Run the code and make sure it works.
 
     // let pairs = vec![(0, 1), (2, 3), (4, 5)];
     // pairs
@@ -19,10 +21,9 @@ fn main() {
     //     .for_each(|t| println!("{:?}", t));
 
     // 3. Uncomment the code below. There is a mutable vector named `numbers`. Use an iterator over
-    // mutable references to multiply each of the values in the numbers in vector by 3 without
-    // consuming the vector.
-    // Hint 1: You'll probably want to use .iter_mut()
-    // Hint 2: `x` will be a mutable reference, so remember to dereference it wherever you use it
+    // mutable references to multiply each of the values in `numbers` by 3.
+    // Hint 1: You'll need .iter_mut() -- bonus points if you use the shorter, syntactic sugar form!
+    // Hint 2: `x` will be a mutable reference, so remember to dereference it to use it
 
     // let mut numbers = vec![1, 2, 3, 4];
     // for x in ... {
@@ -30,6 +31,11 @@ fn main() {
     // }
     // println!("{:?}", numbers); // should print [3, 6, 9, 12]
 
+    let mut numbers = vec![1, 2, 3, 4];
+    numbers.iter_mut().for_each(|x| *x *= 3);
+    println!("{:?}", numbers); // should print [3, 6, 9, 12]
+
+
     // 4. Uncomment the code below.  Take the vector of words and
     // - Convert the vector into an iterator with .into_iter()
     // - Use .filter() to remove any word that contains the letter "h" -- use .contains()
@@ -42,15 +48,9 @@ fn main() {
     // let transformed...  // do the stuff here
     // println!("Transformed: {:?}", transformed);
 
-    // Challenge: Both .iter() and .iter_mut() can be used via shorter "syntactic sugar" in a
-    // for-loop definition. For example, instead of:
+    // Challenge:
     //
-    //     for x in vector.iter() { ... }
-    //
-    // you can do:
-    //
-    //     for x in &vector { ... }
-    //
-    // Can you figure out how to change .iter_mut() in #3 to the shorter, syntactic sugar form for
-    // mutable references?
+    // - Rewrite the code in #2 as a for loop
+    // - Rewrite the code in #3 in functional style (without a for loop).  Hint: There are multiple
+    // ways to accomplish this, but they all end with an iterator consumer.
 }