swift-optionals-4.swift

// Non-optional vars

var mutableBeverage = "Leffe"
println(mutableBeverage) // "Leffe"

mutableBeverage = "Bud"
println(mutableBeverage) // "Bud"

mutableBeverage = mutableBeverage + "weiser"
println(mutableBeverage) // "Budweiser"

mutableBeverage = nil // Compiler error

// Optional vars

var mutableCostume: String? = "Dracula"
println(mutableCostume) // Optional("Dracula")

mutableCostume = "Frankenstein"
println(mutableCostume) // Optional("Frankenstein")

mutableCostume = "Bride of " + mutableCostume!
println(mutableCostume) // Optional("Bride of Frankenstein")

mutableCostume = nil // nil

// Non-optional lets

let immutableBeverage = "Bud"
println(immutableBeverage) // "Bud"

immutableBeverage = "Leffe" // Compiler error

immutableBeverage = immutableBeverage + "weiser" // Compiler error

immutableBeverage = nil // Compiler error

// Optional lets

let immutableCostume: String? = "Dracula"
println(immutableCostume) // Optional("Dracula")

immutableCostume = "Frankenstein" // Compiler error

immutableCostume = "Bride of " + immutableName! // Compiler error

immutableCostume = nil // Compiler error

let anotherCostume: String? = nil 
println(anotherCostume) // nil