# Lessons from Stack 1

When you need to do the ol' switcheroo with some memory
mem::replace comes in useful.

# Lessons from Stack 2

take() is handy, read more about this.
Sometimes you just have to get your hands dirty and do some lifetimes, just a fact of life, get used to it son.
Revise some of these impl types, to understand better how they function with std library collections.

# Lessons from Stack 3

and_then(<closure>) allows you to map over a value returning an option.
Useful for when the type mapping is an option.

# Lessons from Stack 4

It's important to conceptualise the invariants before you write code to validate assumptions and edge cases.
borrow() and borrow_mut() are important methods when using RefCell.
Drop can be implemented with `popping` until no elements are left.