more ch4 progress

ch4/ownership/src/main.rs

@@ -52,12 +52,16 @@ fn main() {
     //   When variable owns a box, when Rust deallocates the variable's frame,
     //   then Rust deallocates the box's heap memory.
     let d = Box::new([0; 1_000_000]); // d owns this Box here
-    let e = d; // e has ownership of the box transfered to it from d
+    let e = d; // e has ownership of the box transfered to it from d. Say it's moved
 
     // Rust data structures like String, Vec, and HashMap use Boxes.
 
-    // Stopped here for the night:
-    // https://rust-book.cs.brown.edu/ch04-01-what-is-ownership.html#variables-cannot-be-used-after-being-moved
+    // Variables can't be used after moving
+    // Can use .clone() to avoid moving data
+    let first = String::from("Ferris");
+    let first_clone = first.clone();
+    let full = add_suffix(first_clone);
+    println!("{full}, originally {first}");
 }
 
 fn plus_one(x: i32) -> i32 {
@@ -67,3 +71,8 @@ fn plus_one(x: i32) -> i32 {
 fn make_and_drop() {
     let a_box = Box::new(5);
 }
+
+fn add_suffix(mut name: String) -> String {
+    name.push_str(" Jr. ");
+    name
+}

ch4/refs_and_borrow/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "refs_and_borrow"
+version = "0.1.0"

ch4/refs_and_borrow/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "refs_and_borrow"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

ch4/refs_and_borrow/src/main.rs

@@ -0,0 +1,26 @@
+fn main() {
+    // These lines wont work bc m1 and m2 are moved
+    // let m1 = String::from("Hello");
+    // let m2 = String::from("World");
+    // greet(m1, m2);
+    // let s = format!("{} {}", m1, m2);
+
+    // This is suboptimal
+    let m1 = String::from("Hello");
+    let m2 = String::from("World");
+    let (m1_again, m2_again) = greet_ret(m1, m2);
+    let s = format!("{} {}", m1_again, m2_again);
+    println!("{s}");
+
+    // stopped here:
+    // https://rust-book.cs.brown.edu/ch04-02-references-and-borrowing.html#references-are-non-owning-pointers
+}
+
+fn greet(g1: String, g2: String) {
+    println!("{} {}!", g1, g2);
+}
+
+fn greet_ret(g1: String, g2: String) -> (String, String) {
+    println!("{} {}!", g1, g2);
+    (g1, g2)
+}