use broom::prelude::*;

// The type you want the heap to contain
pub enum Object {
    Num(f64),
    List(Vec<Handle<Self>>),
}

// Tell the garbage collector how to explore a graph of this object
impl Trace<Self> for Object {
    fn trace(&self, tracer: &mut Tracer<Self>) {
        match self {
            Object::Num(_) => {},
            Object::List(objects) => objects.trace(tracer),
        }
    }
}

// Create a new heap
let mut heap = Heap::default();

// Temporary objects are cheaper than rooted objects, but don't survive heap cleans
let a = heap.insert_temp(Object::Num(42.0));
let b = heap.insert_temp(Object::Num(1337.0));

// Turn the numbers into a rooted list
let c = heap.insert(Object::List(vec![a, b]));

// Change one of the numbers - this is safe, even if the object is self-referential!
*heap.get_mut(a).unwrap() = Object::Num(256.0);

// Create another number object
let d = heap.insert_temp(Object::Num(0.0));

// Clean up unused heap objects
heap.clean();

// a, b and c are all kept alive because c is rooted and a and b are its children
assert!(heap.contains(a));
assert!(heap.contains(b));
assert!(heap.contains(c));

// Because `d` was temporary and unused, it did not survive the heap clean
assert!(!heap.contains(d));