Arc1 code added

standard_library_types/arc1.rs

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+// make this code compile and don't create any copies of the "numbers" Vec.
+// scroll down for hints
+
+use std::sync::Arc;
+use std::thread;
+
+fn main() {
+    let numbers: Vec<_> = (0..100u32).collect();
+    let shared_numbers = // TODO
+    let mut joinhandles = Vec::new();
+
+    for offset in 0..5 {
+        joinhandles.push(
+        thread::spawn(move || {
+            let mut i = offset;
+            let mut sum = 0;
+            while i<child_numbers.len() {
+                sum += child_numbers[i];
+                i += 5;
+            }
+            println!("Sum of offset {} is {}", offset, sum);
+        }));
+    }
+    for handle in joinhandles.into_iter() {
+        handle.join().unwrap();
+    }
+}
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+// In line 6 you must create an Arc from the numbers vector.
+// You must create the child_numbers inside the loop but still in the main thread.
+// child_numbers is a clone of the Arc of the numbers, not a copy of the numbers.