finish ch4, come back later

ch4/fixing_ownership_issues/Cargo.lock

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

ch4/fixing_ownership_issues/Cargo.toml

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

ch4/fixing_ownership_issues/src/main.rs

@@ -0,0 +1,113 @@
+// This section covers some common ownership errors.
+// I'll probably have to come back to this section. I'm not enjoying
+// this part of Rust so learning this is not my favorite.
+
+use std::rc::Rc;
+
+fn main() {
+    // ------------------------------------------------------------------------
+    // fixing an unsafe program: not enough permissions
+
+    let name = vec![String::from("Ferris!")];
+    let first = &name[0];
+    stringify_name_with_title(&name);
+    println!("{}", first);
+
+    // ------------------------------------------------------------------------
+    // fixing an unsafe program: copying vs. moving out of a collection
+
+    let v: Vec<i32> = vec![0, 1, 2];
+    let n_ref: &i32 = &v[0];
+    let n: i32 = *n_ref;
+
+    // If a value does not own head data, then it can be copied without a move
+    // Unlike what's happening below
+    // i32 doesn't own head data, so it can be copied without a move
+    // String does own heap data, so it can't be copied without a move
+    // &String doesn't own heap data, so it can be copied without a move
+    // Solution 1: Avoid taking ownership with immutable reference
+    let vs: Vec<String> = vec![String::from("Hello world")];
+    let s_ref: &String = &vs[0];
+    // let s: String = *s_ref;
+    println!("{s_ref}");
+    // Solution 2: Clone the data if want ownership
+    // Solution 3: Use Vec::remove to move string out of the vector
+
+    // ------------------------------------------------------------------------
+    // fixing an safe program: mutating different tuple fields
+
+    let mut name = (String::from("Ferris"), String::from("Rustacean"));
+    let first = &name.0;
+    name.1.push_str(", Esq.");
+    println!("{first} {}", name.1);
+}
+
+// fixing an unsafe program: returing a reference to the stack
+// fn return_a_string() -> &String {
+//     let s = String::from("Hello World");
+//     &s
+// fails because this function will get allocated but s is owned by this function.
+// }
+
+fn return_a_string_diff_owner() -> String {
+    let s = String::from("Hello world");
+    s
+}
+
+// static means it lives forever
+fn return_a_string_static() -> &'static str {
+    "Hello world"
+}
+
+// rc is a reference-counted pointer. More in ch14
+// only clones a pointer to s and not the data itself
+fn return_a_string_rc() -> Rc<String> {
+    let s = Rc::new(String::from("Hello world"));
+    Rc::clone(&s)
+}
+
+// caller provides a slot with a mutable reference
+fn return_a_string_slot(output: &mut String) {
+    output.replace_range(.., "Hello world");
+}
+
+// fixing an unsafe program: not enough permissions
+// Replace "&Vec<String>" with "$mut Vec<String>". THIS IS NOT A GOOD SOLUTION!
+// Functions shouldn't mutate their inputs if the caller would not expect it.
+// Basically just don't use mut in functions. Make a copy of the variable instead
+// if mutating it.
+fn stringify_name_with_title(name: &Vec<String>) -> String {
+    let mut name_clone = name.clone();
+    name_clone.push(String::from("Esq."));
+    let full = name_clone.join(" ");
+    full
+}
+
+fn stringify_name_with_title_final(name: &Vec<String>) -> String {
+    let mut full = name.join(" ");
+    full.push_str(" Esq.");
+    full
+}
+
+// fixing an unsafe program: aliasing and mutating a data structure
+// This function fails
+// fn add_big_strings(dst: &mut Vec<String>, src: &[String]) {
+//     let largest: &String = dst.iter().max_by_key(|s| s.len()).unwrap();
+//     for s in src {
+//         if s.len() > largest.len() {
+//             dst.push(s.clone());
+//         }
+//     }
+// }
+
+// The fix for above since we only need the length
+// Shortens the lifetime of borrows on dst to not overlap with
+//   mutation to dst.
+fn add_big_strings(dst: &mut Vec<String>, src: &[String]) {
+    let largest_len: usize = dst.iter().max_by_key(|s| s.len()).unwrap().len();
+    for s in src {
+        if s.len() > largest_len {
+            dst.push(s.clone());
+        }
+    }
+}

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) {

ch4/slice_type/Cargo.lock

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

ch4/slice_type/Cargo.toml

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

ch4/slice_type/src/main.rs

@@ -0,0 +1,54 @@
+// Section 4.4
+// slices allow for reference in contiguous sequences of elements
+// inside of a collection.
+//
+// Part of writing fast Rust code is also understanding how
+// allocations work. This portion of the book is important, and I
+// need to come back and read it later.
+
+fn main() {
+    let mut s = String::from("hello world");
+    let word = first_word(&s);
+
+    // borrowed here. Not allowed
+    // s.clear();
+    // print!("word: {word}");
+
+    // Range syntax. the .. like Haskell
+    let s = String::from("hello");
+    let slice = &s[0..2];
+    let slice = &s[..2];
+    let slice = &s[..]; // can just slice the whole thing
+
+    // Is this possible?
+    // no
+    // let temp_arr_size = 5;
+    // let temparr = [1; temp_arr_size];
+}
+
+// This isn't part of the section, just me testing out ownership
+fn mod_string(s: &mut String) -> &String {
+    s.push_str("hello");
+    s
+}
+
+fn first_word(s: &String) -> &str {
+    let bytes = s.as_bytes();
+    for (i, &item) in bytes.iter().enumerate() {
+        if item == b' ' {
+            return &s[0..i];
+        }
+    }
+    &s[..]
+}
+
+// as.bytes() makes this an immutable reference
+// fn example_test() {
+//     let mut s = String::from("hello");
+//     for &item in s.as_bytes().iter() {
+//         if item == b'l' {
+//             s.push_str(" world");
+//         }
+//     }
+//     println!("{s}");
+// }