Swift Programming: The Big Nerd Ranch Guide

Type Constraint where Clauses

Write a new function that takes every element of an array and pushes it onto a stack.

Listing 22.17  Pushing items from an array onto a stack

...
func pushItemsOntoStack<Element>(inout stack: Stack<Element>,
                                            fromArray array: [Element]) {
    for item in array {
        stack.push(item)
    }
}

pushItemsOntoStack(&myStack, fromArray: [1, 2, 3])
for value in myStack {
    print("after pushing: got \(value)")
}

pushItemsOntoStack(_:fromArray:) takes its first argument, a Stack, as an inout argument so that it can call the mutating method push(_:). This function is useful, but it is not as general as it could be. You now know that any type that conforms to SequenceType can be used in a for ... in loop, so why should this ...