Stacks are abstract Data Structrues. This means they are natively in a programming language such as Swift. Stacks also follow LIFO (Last in first out), what this means is the last item that is entered into the Stack is the first item to the leave the stack.
Stacks are used to enforce the way data is acessed. They are created using arrays as containers. Having arrays as the data container provides with certain properties and methods for free. Methods such append and popLast. And properties such as isEmpty.
public mutating func push(value:T){
container.append(value)
}public mutating func pop() -> T? {
return container.popLast()
}This method allows to take a look at the item on the top of the stack with out removing the item
public var peek:T? {
return container.last
}