Add code

example_8/src/main.rs

@@ -0,0 +1,23 @@
+use std::rc::Rc; // reference-counted, non atomic
+use std::sync::Arc; // reference-counted, atomic
+
+fn main() {
+    // this will not compile:
+    let rc = Rc::new("not thread safe");
+    std::thread::spawn(move || {
+        println!("I have an rc with: {}", rc);
+    });
+
+    // this compiles fine:
+    let arc = Arc::new("thread safe");
+    std::thread::spawn(move || {
+        println!("I have an arc with: {}", arc);
+    });
+
+    // this will also not compile:
+    let mut v = Vec::new();
+    std::thread::spawn(|| {
+        v.push(42);
+    });
+    let _ = v.pop();
+}