expand dbg! example usage

Author: mikemorris

src/ch05-02-example-structs.md

@@ -256,7 +256,9 @@ Now that we're familiar with deriving the `Debug` trait for helpful `println!`
 formatting, let's take a look at a macro that builds on top of that functionality.
 The `dbg!` macro (available in Rust 1.32.0 and later) can accept any argument
 that implements the `Debug` trait, and will print helpful debugging context in
-the same style as `println!("{:?#}", rect1)`, plus the filename and line number.
+the same style as `println!("{:#?}", rect1)`, plus the filename, line number and
+argument name. `dbg!` takes ownership of (and returns a clone of) the argument
+passed to it, and so can even be used inline to wrap most references or values.
 
 <span class="filename">Filename: src/main.rs</span>
 
@@ -267,11 +269,38 @@ struct Rectangle {
     height: u32,
 }
 
+fn get_width(rect: &Rectangle) -> u32 {
+    rect.width
+}
+
+fn get_height(rect: Rectangle) -> u32 {
+    rect.height
+}
+
 fn main() {
-    let rect1 = Rectangle { width: 30, height: 50 };
+    let rect1 = Rectangle {
+        width: 30,
+        height: 50,
+    };
 
-    dbg!(rect1);
+    println!("width: {}", get_width(dbg!(&rect1)));
+    println!("height: {}", get_height(dbg!(rect1)));
+}
+```
+
+Now when we run the program, we’ll see the following output:
+
+```text
+[src/main.rs:21] &rect1 = Rectangle {
+    width: 30,
+    height: 50,
+}
+width: 30
+[src/main.rs:22] rect1 = Rectangle {
+    width: 30,
+    height: 50,
 }
+height: 50
 ```
 
 Rust has provided a number of traits for us to use with the `derive` annotation