Update Ch15

projects/rc_demo/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "rc_demo"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

projects/rc_demo/src/main.rs

@@ -0,0 +1,17 @@
+use std::rc::Rc;
+
+#[derive(Debug)]
+enum List {
+    Cons(i32, Rc<List>),
+    Nil,
+}
+
+use crate::List::{Cons, Nil};
+
+fn main() {
+    let a = Rc::new(Cons(5, Rc::new(Cons(10, Rc::new(Nil)))));
+    let b = Cons(3, Rc::clone(&a));
+    let c = Cons(4, Rc::clone(&a));
+
+    println! ("b 为: {:?}\nc 为： {:?}", b, c);
+}