started ch15.04

ch15/sect-deref/src/main.rs

@@ -23,6 +23,10 @@ impl<T> Deref for MyBox<T> {
     }
 }
 
+fn hello(name: &str) {
+    println!("Hello, {name}!");
+}
+
 fn main() {
     // following the pointer to the value
     let x = 5;
@@ -51,6 +55,17 @@ fn main() {
     // deref coercion converts a reference to a type that implements
     // Deref trait into a reference to another type.
 
-    // stopped here:
+    let m = MyBox::new(String::from("Rust"));
-    // https://rust-book.cs.brown.edu/ch15-02-deref.html#implicit-deref-coercions-with-functions-and-methods
+    hello(&m);
+
+    // How deref coercion interacts with mutability
+    //
+    // Rust does deref coercion when it finds types and
+    // trait implementations in three cases:
+    // 1) From &T to &U when `T: Deref<Target=U>`
+    // 2) From &mut T to &mut U when `T: DerefMut<Target=U>`
+    // 3) From &mut T to &U when `T: Deref<Target=U>`
+    //
+    // Rust will never coerce an immutable reference into a
+    // mutable reference.
 }

ch15/sect-drop/Cargo.lock

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

ch15/sect-drop/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "sect-drop"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

ch15/sect-drop/src/main.rs

@@ -0,0 +1,34 @@
+//! # Running Code on Cleanup with the Drop Trait
+//!
+//! Second trait important to the smart pointer is `Drop`, lets
+//! customize what happens when value is about to go out of scope.
+
+use std::mem::drop;
+
+struct CustomSmartPointer {
+    data: String,
+}
+
+impl Drop for CustomSmartPointer {
+    fn drop(&mut self) {
+        println!("Dropping CustomSmartPointer with data `{}`!", self.data);
+    }
+}
+
+fn main() {
+    let c = CustomSmartPointer {
+        data: String::from("my stuff"),
+    };
+    let d = CustomSmartPointer {
+        data: String::from("other stuff"),
+    };
+    println!("CustomSmartPointers created.");
+
+    let c = CustomSmartPointer {
+        data: String::from("some data"),
+    };
+    println!("CustomSmartPointer created.");
+    // c.drop(); // not allowed to explictly call drop like this.
+    drop(c);
+    println!("CustomSmartPointer dropped before the end of main.");
+}

ch15/sect-rc/Cargo.lock

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

ch15/sect-rc/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "sect-rc"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

ch15/sect-rc/src/main.rs

@@ -0,0 +1,6 @@
+//! Stopped here:
+//! https://rust-book.cs.brown.edu/ch15-04-rc.html#rct-the-reference-counted-smart-pointer
+
+fn main() {
+    println!("Hello, world!");
+}