finish ch4.2

ch4/refs_and_borrow/src/main.rs

@@ -100,8 +100,13 @@ fn main() {
     // -----------------------------------------------------------------------------
     // Data must outlive all of its references
 
-    // Ended at:
-    // https://rust-book.cs.brown.edu/ch04-02-references-and-borrowing.html#summary
+    // -----------------------------------------------------------------------------
+    // Summary
+
+    // References provide ability to read/write data with consuming ownership.
+    // References created with borrows (& and &mut) used dereferenced with * (often implictly)
+
+    // Off to fixing ownership issues in ch4.3
 }
 
 fn greet(g1: String, g2: String) {