Turn a Box into a BoxAllocation about copyless HOT 5 OPEN

struct Animal {
	age: u32,
	weight: f32,
	height: f32,
	number_of_legs: u32,
	a lot of other fields, making this a huge struct...
}

fn parse_animal_from_file(filename: String) -> Box<Animal> {
	let file = open(filename);
	let age = file.parse_age();
	let weight = file.parse_weight();
	...
	BoxAllocation<Animal>::alloc().init(Animal {age, weight, height, etc.})
}

let dog_data = parse_animal_from_file("dog.txt");
print("{:?}", dog_data);
// Note that dog_data is no longer used past this point.
let cat_data = parse_animal_from_file("cat.txt");
print("{:?}", cat_data);

fn parse_animal_from_file(filename: String, box_alloc: BoxAllocation<Animal>) -> Box<Animal> {
	let file = open(filename);
	let age = file.parse_age();
	let weight = file.parse_weight();
	...
	box_alloc.init(Animal {age, weight, height, etc.})
}

let box_alloc = BoxAllocation<Thing>::alloc();
let dog_data = parse_animal_from_file("dog.txt", box_alloc);
print("{:?}", dog_data);
let box_alloc = dog_data.turn_back_into_alloc();
let cat_data = parse_animal_from_file("cat.txt", box_alloc);
print("{:?}", cat_data);