initial commit

exercises/07_threads/06_interior_mutability/Cargo.toml

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+[package]
+name = "interior_mutability"
+version = "0.1.0"
+edition = "2021"

exercises/07_threads/06_interior_mutability/src/lib.rs

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+// TODO: Use `Rc` and `RefCell` to implement `DropTracker<T>`, a wrapper around a value of type `T`
+//  that increments a shared `usize` counter every time the wrapped value is dropped.
+
+use std::cell::RefCell;
+use std::rc::Rc;
+
+pub struct DropTracker<T> {
+    value: T,
+    counter: todo!(),
+}
+
+impl<T> DropTracker<T> {
+    pub fn new(value: T, counter: todo!()) -> Self {
+        Self { value, counter }
+    }
+}
+
+impl<T> Drop for DropTracker<T> {
+    fn drop(&mut self) {
+        todo!()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let counter = Rc::new(RefCell::new(0));
+        let _ = DropTracker::new((), Rc::clone(&counter));
+        assert_eq!(*counter.borrow(), 1);
+    }
+
+    #[test]
+    fn multiple() {
+        let counter = Rc::new(RefCell::new(0));
+
+        {
+            let a = DropTracker::new(5, Rc::clone(&counter));
+            let b = DropTracker::new(6, Rc::clone(&counter));
+        }
+
+        assert_eq!(*counter.borrow(), 2);
+    }
+}