"select" non-nil elements.

select.playground

// "select" non-nil elements.

var data: Array<String> = ["0", "a"]

var wrappedIntsWithOptionals = data.map { $0.toInt() } as Array<Int?>
println("wrappedIntsWithOptionals: \(wrappedIntsWithOptionals)")
// wrappedIntsWithOptionals: [Optional(0), nil]


// ## This works

let wrappedInts = wrappedIntsWithOptionals.filter { $0 != nil } as Array<Int?>
println("wrappedInts: \(wrappedInts)")
// wrappedInts: [Optional(0)]

let mappedToUnwrapped = wrappedInts.map { $0! } as Array<Int>
println("mappedToUnwrapped: \(mappedToUnwrapped)")
// mappedToUnwrapped: [0]


// ## This does not

let unwrappedInts = wrappedIntsWithOptionals.filter { $0 != nil } as Array<Int>
// fatal error: can't unsafeBitCast between types of different sizes
println("unwrappedInts: \(unwrappedInts)")