What is the difference between reference and Box in Rust?
In Rust, a reference is a pointer to a value that is owned by another variable or data structure, while a Box is a data structure that owns a value and provides a way to allocate that value on the heap. 

References are used to borrow values without taking ownership of them. They are denoted by an ampersand (`&`) before the variable name. For example:

```
let x = 5;
let y = &x; // y is a reference to x
```

In this example, `y` is a reference to the value of `x`. The reference `y` can be used to read the value of `x`, but it cannot be used to modify the value of `x` directly.

On the other hand, a Box is a data structure that allocates memory on the heap and stores a value there. A Box is created using the `Box::new()` function, and can be dereferenced using the `*` operator. For example:

```
let x = Box::new(5);
let y = *x; // y is a copy of the value in x
```

In this example, `x` is a Box that owns the value `5`. The value can be accessed by dereferencing `x` using the `*` operator, as shown in the assignment to `y`.

The main difference between a reference and a Box is ownership. A reference does not own the value it points to, while a Box does. This means that a reference cannot be moved or modified, while a Box can. Additionally, a Box can be used to allocate values on the heap, which can be useful in situations where the size of the value is not known at compile time or where the value needs to be shared between multiple parts of a program.
In what situations would I want to use a reference vs a box?
Situations where you may want to use a reference rather than a Box are as follows:

- Avoid moving data around in memory, which can improve performance.
- Access or modify the same data in different parts of your code without transferring ownership.
- Implement functions that works with borrowed data rather than passing the entire data to the function.

While cases where you may want to use a Box rather than a reference are:

- When you have a large data structure and want to transfer ownership without copying the data.
- When you need to create recursive data structures, such as linked lists or trees.
- When you want to use trait objects (dynamically dispatched types), which require a heap-allocated, sized container to hold the object.

In summary, use a reference when you want to temporarily access or modify data without taking ownership, and use a Box when you need heap allocation, ownership transfer, or dynamic dispatch.