docs: cleanup the explanation paragraphs at the start of each exercise.

exercises/smart_pointers/arc1.rs

@@ -1,21 +1,24 @@
 // arc1.rs
-// In this exercise, we are given a Vec of u32 called "numbers" with values ranging
-// from 0 to 99 -- [ 0, 1, 2, ..., 98, 99 ]
-// We would like to use this set of numbers within 8 different threads simultaneously.
-// Each thread is going to get the sum of every eighth value, with an offset.
+//
+// In this exercise, we are given a Vec of u32 called "numbers" with values
+// ranging from 0 to 99 -- [ 0, 1, 2, ..., 98, 99 ] We would like to use this
+// set of numbers within 8 different threads simultaneously. Each thread is
+// going to get the sum of every eighth value, with an offset.
+//
 // The first thread (offset 0), will sum 0, 8, 16, ...
 // The second thread (offset 1), will sum 1, 9, 17, ...
 // The third thread (offset 2), will sum 2, 10, 18, ...
 // ...
 // The eighth thread (offset 7), will sum 7, 15, 23, ...
-
+//
 // Because we are using threads, our values need to be thread-safe.  Therefore,
 // we are using Arc.  We need to make a change in each of the two TODOs.
-
-
+//
 // Make this code compile by filling in a value for `shared_numbers` where the
 // first TODO comment is, and create an initial binding for `child_numbers`
-// where the second TODO comment is. Try not to create any copies of the `numbers` Vec!
+// where the second TODO comment is. Try not to create any copies of the
+// `numbers` Vec!
+//
 // Execute `rustlings hint arc1` or use the `hint` watch subcommand for a hint.
 
 // I AM NOT DONE

exercises/smart_pointers/box1.rs

@@ -1,13 +1,15 @@
 // box1.rs
 //
-// At compile time, Rust needs to know how much space a type takes up. This becomes problematic
-// for recursive types, where a value can have as part of itself another value of the same type.
-// To get around the issue, we can use a `Box` - a smart pointer used to store data on the heap,
-// which also allows us to wrap a recursive type.
+// At compile time, Rust needs to know how much space a type takes up. This
+// becomes problematic for recursive types, where a value can have as part of
+// itself another value of the same type. To get around the issue, we can use a
+// `Box` - a smart pointer used to store data on the heap, which also allows us
+// to wrap a recursive type.
 //
-// The recursive type we're implementing in this exercise is the `cons list` - a data structure
-// frequently found in functional programming languages. Each item in a cons list contains two
-// elements: the value of the current item and the next item. The last item is a value called `Nil`.
+// The recursive type we're implementing in this exercise is the `cons list` - a
+// data structure frequently found in functional programming languages. Each
+// item in a cons list contains two elements: the value of the current item and
+// the next item. The last item is a value called `Nil`.
 //
 // Step 1: use a `Box` in the enum definition to make the code compile
 // Step 2: create both empty and non-empty cons lists by replacing `todo!()`

exercises/smart_pointers/cow1.rs

@@ -1,12 +1,16 @@
 // cow1.rs
-
-// This exercise explores the Cow, or Clone-On-Write type.
-// Cow is a clone-on-write smart pointer.
-// It can enclose and provide immutable access to borrowed data, and clone the data lazily when mutation or ownership is required.
-// The type is designed to work with general borrowed data via the Borrow trait.
+//
+// This exercise explores the Cow, or Clone-On-Write type. Cow is a
+// clone-on-write smart pointer. It can enclose and provide immutable access to
+// borrowed data, and clone the data lazily when mutation or ownership is
+// required. The type is designed to work with general borrowed data via the
+// Borrow trait.
 //
 // This exercise is meant to show you what to expect when passing data to Cow.
-// Fix the unit tests by checking for Cow::Owned(_) and Cow::Borrowed(_) at the TODO markers.
+// Fix the unit tests by checking for Cow::Owned(_) and Cow::Borrowed(_) at the
+// TODO markers.
+//
+// Execute `rustlings hint cow1` or use the `hint` watch subcommand for a hint.
 
 // I AM NOT DONE
 
@@ -50,10 +54,9 @@ mod tests {
 
     #[test]
     fn owned_no_mutation() -> Result<(), &'static str> {
-        // We can also pass `slice` without `&` so Cow owns it directly.
-        // In this case no mutation occurs and thus also no clone,
-        // but the result is still owned because it was never borrowed
-        // or mutated.
+        // We can also pass `slice` without `&` so Cow owns it directly. In this
+        // case no mutation occurs and thus also no clone, but the result is
+        // still owned because it was never borrowed or mutated.
         let slice = vec![0, 1, 2];
         let mut input = Cow::from(slice);
         match abs_all(&mut input) {
@@ -63,9 +66,9 @@ mod tests {
 
     #[test]
     fn owned_mutation() -> Result<(), &'static str> {
-        // Of course this is also the case if a mutation does occur.
-        // In this case the call to `to_mut()` returns a reference to
-        // the same data as before.
+        // Of course this is also the case if a mutation does occur. In this
+        // case the call to `to_mut()` returns a reference to the same data as
+        // before.
         let slice = vec![-1, 0, 1];
         let mut input = Cow::from(slice);
         match abs_all(&mut input) {

exercises/smart_pointers/rc1.rs

@@ -1,9 +1,14 @@
 // rc1.rs
-// In this exercise, we want to express the concept of multiple owners via the Rc<T> type.
-// This is a model of our solar system - there is a Sun type and multiple Planets.
-// The Planets take ownership of the sun, indicating that they revolve around the sun.
-
-// Make this code compile by using the proper Rc primitives to express that the sun has multiple owners.
+//
+// In this exercise, we want to express the concept of multiple owners via the
+// Rc<T> type. This is a model of our solar system - there is a Sun type and
+// multiple Planets. The Planets take ownership of the sun, indicating that they
+// revolve around the sun.
+//
+// Make this code compile by using the proper Rc primitives to express that the
+// sun has multiple owners.
+//
+// Execute `rustlings hint rc1` or use the `hint` watch subcommand for a hint.
 
 // I AM NOT DONE