Align smart pointer descriptions and links

We now avoid the `<T>` in the page title. We refer to `Rc` and `Arc`
as reference-counted shared pointers that allow access to data from
multiple places or threads.

src/SUMMARY.md

@@ -140,7 +140,7 @@
   - [Exercise: Builder Type](memory-management/exercise.md)
     - [Solution](memory-management/solution.md)
 - [Smart Pointers](smart-pointers.md)
-  - [`Box<T>`](smart-pointers/box.md)
+  - [`Box`](smart-pointers/box.md)
   - [`Rc`](smart-pointers/rc.md)
   - [Owned Trait Objects](smart-pointers/trait-objects.md)
   - [Exercise: Binary Tree](smart-pointers/exercise.md)

src/borrowing/interior-mutability.md

@@ -14,6 +14,8 @@ while still ensuring safety, typically by performing a runtime check.
 
 ## `RefCell`
 
+A [`RefCell<T>`] gives you mutable access to a value behind a shared reference:
+
 ```rust,editable
 use std::cell::RefCell;
 
@@ -36,9 +38,9 @@ fn main() {
 
 ## `Cell`
 
-`Cell` wraps a value and allows getting or setting the value, even with a shared
+[`Cell<T>`] wraps a `T` value. It allows getting or setting the value, even with
-reference to the `Cell`. However, it does not allow any references to the value.
+a shared reference to the `Cell`. However, it does not allow any references to
-Since there are no references, borrowing rules cannot be broken.
+the value. Since there are no references, the borrowing rules cannot be broken.
 
 ```rust,editable
 use std::cell::Cell;
@@ -72,3 +74,6 @@ that safety, and `RefCell` and `Cell` are two of them.
   have its own cost.
 
 </details>
+
+[`Cell<T>`]: https://doc.rust-lang.org/std/cell/struct.Cell.html
+[`RefCell<T>`]: https://doc.rust-lang.org/std/cell/struct.RefCell.html

src/concurrency/shared-state/arc.md

@@ -4,7 +4,8 @@ minutes: 5
 
 # `Arc`
 
-[`Arc<T>`][1] allows shared read-only access via `Arc::clone`:
+[`Arc<T>`] is a reference-counted shared pointer to `T`. Use this when you need
+to refer to the same data from multiple threads:
 
 ```rust,editable
 use std::sync::Arc;
@@ -26,18 +27,21 @@ fn main() {
 }
 ```
 
-[1]: https://doc.rust-lang.org/std/sync/struct.Arc.html
-
 <details>
 
-- `Arc` stands for "Atomic Reference Counted", a thread safe version of `Rc`
+- `Arc` is short for "Atomically Reference Counted". It uses atomic
-  that uses atomic operations.
+  (thread-safe) CPU instructions to maintain the reference count. `Arc` is a
+  thread safe version of [`Rc`].
 - `Arc<T>` implements `Clone` whether or not `T` does. It implements `Send` and
   `Sync` if and only if `T` implements them both.
 - `Arc::clone()` has the cost of atomic operations that get executed, but after
   that the use of the `T` is free.
 - Beware of reference cycles, `Arc` does not use a garbage collector to detect
   them.
-  - `std::sync::Weak` can help.
+  - [`std::sync::Weak`] can help avoid reference cycles.
 
 </details>
+
+[`Arc<T>`]: https://doc.rust-lang.org/std/sync/struct.Arc.html
+[`Rc`]: ../../smart-pointers/rc.md
+[`std::sync::Weak`]: https://doc.rust-lang.org/std/sync/struct.Weak.html

src/concurrency/shared-state/mutex.md

@@ -6,7 +6,7 @@ minutes: 14
 
 [`Mutex<T>`][1] ensures mutual exclusion _and_ allows mutable access to `T`
 behind a read-only interface (another form of
-[interior mutability](../../borrowing/interior-mutability)):
+[interior mutability](../../borrowing/interior-mutability.md)):
 
 ```rust,editable
 use std::sync::Mutex;

src/smart-pointers/box.md

@@ -2,10 +2,10 @@
 minutes: 8
 ---
 
-# `Box<T>`
+# `Box`
 
-[`Box`](https://doc.rust-lang.org/std/boxed/struct.Box.html) is an owned pointer
+[`Box<T>`](https://doc.rust-lang.org/std/boxed/struct.Box.html) is an owned
-to data on the heap:
+pointer to a `T` on the heap:
 
 ```rust,editable
 fn main() {
@@ -28,8 +28,7 @@ fn main() {
 ```
 
 `Box<T>` implements `Deref<Target = T>`, which means that you can
-[call methods
+[call methods from `T` directly](https://doc.rust-lang.org/std/ops/trait.Deref.html#more-on-deref-coercion).
-from `T` directly on a `Box<T>`](https://doc.rust-lang.org/std/ops/trait.Deref.html#more-on-deref-coercion).
 
 Recursive data types or data types with dynamic sizes need to use a `Box`:
 

src/smart-pointers/rc.md

@@ -4,8 +4,8 @@ minutes: 5
 
 # `Rc`
 
-[`Rc`][1] is a reference-counted shared pointer. Use this when you need to refer
+[`Rc<T>`][1] is a reference-counted shared pointer to `T`. Use this when you
-to the same data from multiple places:
+need to refer to the same data from multiple places:
 
 ```rust,editable
 use std::rc::Rc;
@@ -25,7 +25,7 @@ fn main() {
 
 [1]: https://doc.rust-lang.org/std/rc/struct.Rc.html
 [2]: ../concurrency/shared-state/arc.md
-[3]: https://doc.rust-lang.org/std/sync/struct.Mutex.html
+[3]: ../concurrency/shared-state/mutex.md
 [4]: https://doc.rust-lang.org/std/rc/struct.Weak.html
 
 <details>