dude.swift

var array = ["One", "Two", "Three"]
array.append("Four")

// This won't compile, since the above array is specialized
// for strings, meaning that other values can't be inserted:
array.append(5)

// As we pull an element out of the array, we can still treat
// it like a normal string, since we have full type safety.
let characterCount = array[0].count