diff --git a/src/bin/tut4.rs b/src/bin/tut4.rs
index f743435..2894eb6 100644
--- a/src/bin/tut4.rs
+++ b/src/bin/tut4.rs
@@ -1,9 +1,27 @@
-// Fearless Concurrency
+// Generic Programming: Dynamic Polymorphism
 
 #![allow(dead_code)]
 #![allow(unused_imports)]
 
 use rust_tutorial::*;
 
+fn stringify_all(xs: Vec<&dyn ToString>) -> String {
+    let strings: Vec<String> =
+        xs.iter().map(|x| x.to_string()).collect();
+
+    strings.join(", ")
+}
+
 fn main() {
+    let mut stringlike_things: Vec<&dyn ToString> = Vec::new();
+
+    let x1 = "abc";
+    let x2 = 100;
+    let x3 = Person { age: 30, name: "Mary".to_string() };
+
+    stringlike_things.push(&x1);
+    stringlike_things.push(&x2);
+    stringlike_things.push(&x3);
+
+    println!("{}", stringify_all(stringlike_things));
 }