1st

Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "by-example-01-02-01-debug"
+version = "0.1.0"

src/main.rs

@@ -1,3 +1,43 @@
-fn main() {
+#![allow(unused)]
-    println!("Hello, world!");
+
+// This structure cannot be printed either with `fmt::Display` or
+// with `fmt::Debug`.
+struct UnPrintable(i32);
+
+// The `derive` attribute automatically creates the implementation
+// required to make this `struct` printable with `fmt::Debug`.
+#[derive(Debug)]
+struct DebugPrintable(i32);
+
+// Derive the `fmt::Debug` implementation for `Structure`. `Structure`
+// is a structure which contains a single `i32`.
+#[derive(Debug)]
+struct Structure {
+    x: i32,
+}
+
+// Put a `Structure` inside of the structure `Deep`. Make it printable
+// also.
+#[derive(Debug)]
+struct Deep(Structure);
+
+fn main() {
+    // Printing with `{:?}` is similar to with `{}`.
+    println!("{:?} months in a year.", 12);
+    println!(
+        "{1:?} {0:?} is the {actor:?} name.",
+        "Slater",
+        "Christian",
+        actor = "actor's"
+    );
+
+    // `Structure` is printable!
+    println!("Now {:?} will print!", Structure { x: 3 });
+    // The problem with `derive` is there is no control over how
+    // the results look. What if I want this to just show a `7`?
+    println!("Now {:?} will print!", Deep(Structure { x: 7 }));
+
+    let x = Deep(Structure { x: 7 });
+
+    println!("{}", x.0.x);
 }