From: Martin Pitt <martin@piware.de>
Date: Mon, 23 Aug 2021 10:03:33 +0000 (+0200)
Subject: HashMap
X-Git-Url: https://piware.de/gitweb/?p=learn-rust.git;a=commitdiff_plain;h=a8b3fed27dcb4a76333ac93aaa5f4143fe854ef8

HashMap
---

diff --git a/src/main.rs b/src/main.rs
index 396d3f2..ff65a06 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,8 +1,11 @@
 mod word_utils;
 
+use std::collections::HashMap;
+
 use word_utils::{first_word, second_word};
 
 fn main() {
+    // strings and functions
     let s = String::from("Hello world");
     println!("first word: '{}'", first_word(&s));
     println!("second word: '{}'", second_word(&s).unwrap());
@@ -15,6 +18,7 @@ fn main() {
         None => println!("match: second word of '{}' does not exist", s2),
     }
 
+    // vectors
     let v1 = vec![1, 2, 3];
     println!("statically initialized vector: {:?}", v1);
 
@@ -29,4 +33,35 @@ fn main() {
     for el in &v2 {
         println!("{}", el);
     }
+
+    // hash maps
+    let mut scores = HashMap::new();
+    scores.insert("john", 10);
+    scores.insert("mary", 20);
+
+    println!("scores: {:?}", scores);
+
+    // hash map with .collect()
+    let persons = vec![("homer", 42), ("marge", 30)];
+    let collect_scores: HashMap<_, _> = persons.into_iter().collect();
+    println!("collect_scores: {:?}", collect_scores);
+
+    for (p, s) in &collect_scores {
+        println!("person {}: score {}", p, s);
+    }
+
+    println!("john's score: {}", scores.get("john").unwrap());
+    println!("jake's score: {}", scores.get("jake").unwrap_or(&-1));
+
+    // double scores
+    for (_, v) in scores.iter_mut() {
+        *v *= 2;
+    }
+    println!("scores after doubling: {:?}", scores);
+
+    // double scores of immutable hashmap (rebuild it)
+    let collect_scores: HashMap<_, _> = collect_scores.iter()
+        .map(|(k, v)| (k, 2 * v))
+        .collect();
+    println!("collect_scores after rebuilding with doubling: {:?}", collect_scores);
 }