From 464864e09f465be5e3b11e96ff071038c19e623d Mon Sep 17 00:00:00 2001
From: Jordan Gong <jordan.gong@protonmail.com>
Date: Sun, 20 Sep 2020 16:35:13 +0800
Subject: Deref smart pointers

---
 smart_pointer/src/main.rs | 48 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/smart_pointer/src/main.rs b/smart_pointer/src/main.rs
index b19ab5f..d7ed84c 100644
--- a/smart_pointer/src/main.rs
+++ b/smart_pointer/src/main.rs
@@ -4,6 +4,24 @@ enum List {
     Nil,
 }
 
+struct MyBox<T>(T);
+
+impl<T> MyBox<T> {
+    fn new(x: T) -> MyBox<T> {
+        MyBox(x)
+    }
+}
+
+use std::ops::Deref;
+
+impl<T> Deref for MyBox<T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        &self.0
+    }
+}
+
 fn main() {
     // Storing `i32` value on heap
     let b = Box::new(5);
@@ -11,4 +29,34 @@ fn main() {
 
     use crate::List::{Cons, Nil};
     let list = Cons(1, Box::new(Cons(2, Box::new(Cons(3, Box::new(Nil))))));
+
+    // Dereferencing
+    let x = 5;
+    let y = &x;
+
+    assert_eq!(5, x);
+    assert_eq!(5, *y);
+
+    let x = 5;
+    let y = Box::new(x);
+
+    assert_eq!(5, x);
+    assert_eq!(5, *y);
+
+    let x = 5;
+    let y = MyBox::new(x);
+
+    assert_eq!(5, x);
+    assert_eq!(5, *y); // `*y` is equivalent to `*(y.deref())`
+
+    fn hello(name: &str) {
+        println!("Hello, {}", name);
+    }
+
+    // Deref coercion
+    let m = MyBox::new(String::from("Rust"));
+    // `&MyBox<String>` -> `&String` -> `&str`
+    hello(&m);
+    // `m`: MyBox<String>, `*m`: String, `(*m)[..]`: str, `&(*m)[..]`: &str
+    hello(&(*m)[..]);
 }
-- 
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