Each MutableBinaryHeapNode needs to be explicitly parameterised or they can end up being parameterised by a type that doesn't match the Heap when T is not concrete, and then Julia will (rightly) throw a conversion error when trying to add them to MutableBinaryHeap's nodes field.
Each MutableBinaryHeapNode needs to be explicitly parameterised or they can end up being parameterised by a type that doesn't match the Heap when T is not concrete, and then Julia will (rightly) throw a conversion error when trying to add them to MutableBinaryHeap's nodes field.