arc1 solution

exercises/19_smart_pointers/arc1.rs

@@ -1,39 +1,42 @@
-// In this exercise, we are given a Vec of u32 called "numbers" with values
-// ranging from 0 to 99 -- [ 0, 1, 2, ..., 98, 99 ] We would like to use this
-// set of numbers within 8 different threads simultaneously. Each thread is
-// going to get the sum of every eighth value, with an offset.
+// In this exercise, we are given a `Vec` of u32 called `numbers` with values
+// ranging from 0 to 99. We would like to use this set of numbers within 8
+// different threads simultaneously. Each thread is going to get the sum of
+// every eighth value with an offset.
 //
-// The first thread (offset 0), will sum 0, 8, 16, ...
-// The second thread (offset 1), will sum 1, 9, 17, ...
-// The third thread (offset 2), will sum 2, 10, 18, ...
-// ...
-// The eighth thread (offset 7), will sum 7, 15, 23, ...
+// The first thread (offset 0), will sum 0, 8, 16, …
+// The second thread (offset 1), will sum 1, 9, 17, …
+// The third thread (offset 2), will sum 2, 10, 18, …
+// …
+// The eighth thread (offset 7), will sum 7, 15, 23, …
 //
 // Because we are using threads, our values need to be thread-safe. Therefore,
-// we are using Arc.  We need to make a change in each of the two TODOs.
-//
-// Make this code compile by filling in a value for `shared_numbers` where the
-// first TODO comment is, and create an initial binding for `child_numbers`
-// where the second TODO comment is. Try not to create any copies of the
-// `numbers` Vec!
+// we are using `Arc`.
 
-#![forbid(unused_imports)] // Do not change this, (or the next) line.
-use std::sync::Arc;
-use std::thread;
+// Don't change the lines below.
+#![forbid(unused_imports)]
+use std::{sync::Arc, thread};
 
 fn main() {
     let numbers: Vec<_> = (0..100u32).collect();
-    let shared_numbers = // TODO
-    let mut joinhandles = Vec::new();
+
+    // TODO: Define `shared_numbers` by using `Arc`.
+    // let shared_numbers = ???;
+
+    let mut join_handles = Vec::new();
 
     for offset in 0..8 {
-        let child_numbers = // TODO
-        joinhandles.push(thread::spawn(move || {
+        // TODO: Define `child_numbers` using `shared_numbers`.
+        // let child_numbers = ???;
+
+        let handle = thread::spawn(move || {
             let sum: u32 = child_numbers.iter().filter(|&&n| n % 8 == offset).sum();
-            println!("Sum of offset {} is {}", offset, sum);
-        }));
+            println!("Sum of offset {offset} is {sum}");
+        });
+
+        join_handles.push(handle);
     }
-    for handle in joinhandles.into_iter() {
+
+    for handle in join_handles.into_iter() {
         handle.join().unwrap();
     }
 }

rustlings-macros/info.toml

@@ -1004,7 +1004,7 @@ name = "arc1"
 dir = "19_smart_pointers"
 test = false
 hint = """
-Make `shared_numbers` be an `Arc` from the numbers vector. Then, in order
+Make `shared_numbers` be an `Arc` from the `numbers` vector. Then, in order
 to avoid creating a copy of `numbers`, you'll need to create `child_numbers`
 inside the loop but still in the main thread.
 

solutions/19_smart_pointers/arc1.rs

@@ -1 +1,42 @@
-// Solutions will be available before the stable release. Thank you for testing the beta version 🥰
+// In this exercise, we are given a `Vec` of u32 called `numbers` with values
+// ranging from 0 to 99. We would like to use this set of numbers within 8
+// different threads simultaneously. Each thread is going to get the sum of
+// every eighth value with an offset.
+//
+// The first thread (offset 0), will sum 0, 8, 16, …
+// The second thread (offset 1), will sum 1, 9, 17, …
+// The third thread (offset 2), will sum 2, 10, 18, …
+// …
+// The eighth thread (offset 7), will sum 7, 15, 23, …
+//
+// Because we are using threads, our values need to be thread-safe. Therefore,
+// we are using `Arc`.
+
+// Don't change the lines below.
+#![forbid(unused_imports)]
+use std::{sync::Arc, thread};
+
+fn main() {
+    let numbers: Vec<_> = (0..100u32).collect();
+
+    let shared_numbers = Arc::new(numbers);
+    //                   ^^^^^^^^^^^^^^^^^
+
+    let mut join_handles = Vec::new();
+
+    for offset in 0..8 {
+        let child_numbers = Arc::clone(&shared_numbers);
+        //                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+        let handle = thread::spawn(move || {
+            let sum: u32 = child_numbers.iter().filter(|&&n| n % 8 == offset).sum();
+            println!("Sum of offset {offset} is {sum}");
+        });
+
+        join_handles.push(handle);
+    }
+
+    for handle in join_handles.into_iter() {
+        handle.join().unwrap();
+    }
+}