ch8 done

ch8/hash-maps/Cargo.lock

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

ch8/hash-maps/Cargo.toml

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

ch8/hash-maps/src/main.rs

@@ -0,0 +1,66 @@
+use std::collections::HashMap;
+
+fn main() {
+    let mut scores = HashMap::new();
+
+    scores.insert(String::from("Blue"), 10);
+    scores.insert(String::from("Yellow"), 50);
+
+    let team_name = String::from("Blue");
+    let score = scores.get(&team_name).copied().unwrap_or(0);
+
+    for (key, value) in &scores {
+        println!("{key}: {value}");
+    }
+
+    // hash maps and ownership
+    // Copy trait implementers copy the values into the hash map.
+    // Owned values like String, values get moved
+
+    let field_name = String::from("Favorite color");
+    let field_value = String::from("Blue");
+
+    let mut map = HashMap::new();
+    map.insert(field_name, field_value);
+
+    // Below is invalid use after move
+    // println!("{field_name}");
+
+    // Updating a hash map
+
+    // overwriting
+
+    let mut scores = HashMap::new();
+
+    scores.insert(String::from("Blue"), 10);
+    scores.insert(String::from("Blue"), 20);
+
+    println!("{scores:?}");
+
+    // adding a key and value only if a key isn't present
+    let mut scores = HashMap::new();
+    scores.insert(String::from("Blue"), 10);
+
+    scores.entry(String::from("Yellow")).or_insert(50);
+    scores.entry(String::from("Blue")).or_insert(50);
+
+    println!("{scores:?}");
+
+    // updating a value based on the old value
+
+    let text = "hello world wonderful world";
+    let mut map = HashMap::new();
+
+    for word in text.split_whitespace() {
+        let count = map.entry(word).or_insert(0);
+        *count += 1;
+    }
+
+    println!("{map:?}");
+
+    // Custom hashing functions
+    //
+    // Why: Default one is secure but kinda slow
+    // Can use a different hashing function if too slow
+    // Talks about how in chapter 10.
+}

ch8/strings/src/main.rs

@@ -26,6 +26,8 @@ fn main() {
 
     let s_total = format!("{s1}-{s2}-{s3}");
 
-    // stopped here:
+    // Rust doesn't allow indexing of Strings.
-    // https://rust-book.cs.brown.edu/ch08-02-strings.html#internal-representation
+    // UTF-8 characters can take over 2 bytes which makes it
+    // not nice for indexing. For rush, just use a vec of chars
+    // straight for the string list.
 }