Swift’s
 Pointy Bits

Unsafe
 Pointer
 Types

Unsafe

“Safe”

let ages = [13.3, 17.5, 18.9, 21.2]

let ages = [13.3, 17.5, 18.9, 21.2] let firstPlusOne = ages.first + 1

let ages = [13.3, 17.5, 18.9, 21.2] let firstPlusOne = ages.first + 1 Value of optional type ‘Int?’ not unwrapped; did you mean to use ‘!’ or ‘?’

let ages = [13.3, 17.5, 18.9, 21.2] let firstPlusOne = ages.first! + 1 // firstPlusOne = 14.3

let ages: [Double] = [] let firstPlusOne = ages.first! + 1

let ages: [Double] = [] let firstPlusOne = ages.first! + 1 ! error: Execution was interrupted, reason: EXC_BAD_INSTRUCTION (code=

let ages = [13.3, 17.5, 18.9, 21.2] let average = ages.reduce(0, +) /
 Double(ages.count) // average = 17.725

let ages: [Double] = [] let average = ages.reduce(0, +) /
 Double(ages.count)

let ages: [Double] = [] let average = ages.reduce(0, +) / 0

let ages: [Double] = [] let average = ages.reduce(0, +) / 0 ! error: Execution was interrupted, reason: EXC_BAD_INSTRUCTION (code= ed: This doesn’t actually crash, but would for [Int]

let ages = [13.3, 17.5, 18.9, 21.2] let last = ages[4]

let ages = [13.3, 17.5, 18.9, 21.2] let last = ages[4] // off by one

let ages = [13.3, 17.5, 18.9, 21.2] let last = ages[4] // off by one error: Execution was interrupted, reason: EXC_BAD_INSTRUCTION (code= !

“Safe”

let ages = [13.3, 17.5, 18.9, 21.2] let last = ages[4] // off by one

let ages = [13.3, 17.5, 18.9, 21.2] let last = ages[4] // off by one // sure, fine, whatever

let ages = [13.3, 17.5, 18.9, 21.2] let last = ages[4] // off by one // last == ???

Unexpected Behavior

10110001 10000001 11001111 00011000 10001110 00010110 00100100 00000000 10110001 10000001 11001111 00011000 10001110 00010110 00100100 00000000 01101000 00001010 10000001 10100110 00010000 01101000 00001010 00000001 10101010 10101010 10101010 10101010 10101010 10101010 10101010 00001010 00000101 00000000 00000000 00000000 00000000 00000000 00000000 00000000 11111000 00100111 11101111 00010100 00000001 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 01111010 00000000 01100001 00000000 01110000 00000000 00100000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 01101100 01101111 01100001 01100100 00100000 01100110 01110010 01101111 01101101 00100000 01101101 01101001 01110011 01100001 01101100 01101001 01100111 01101110 01100101 01100100 00100000 01110010 01100001 01110111 00100000 01110000 01101111 01101001 01101110 01110100 01100101 01110010 00000000 01100110 01100001 01110100 01100001 01101100 00100000 01100101 01110010 01110010 01101111 01110010 00000000 00000000 00000000 00000000 01101001 01101110 01110110 01100001 01101100 01101001 01100100 00100000 01110101 01101110 01110011 01100001 01100110 01100101 01000100 01101111 01110111 01101110 01100011 01100001 01110011 01110100 00000000 00000000

B1 81 CF 18 8E 16 24 00 B1 81 CF 18 8E 16 24 00 68 0A 81 A6 10 68 0A 01 AA AA AA AA AA AA AA 0A 05 00 00 00 00 00 00 00 18 18 4F 12 01 00 00 00 00 00 00 00 00 00 00 00 7A 00 61 00 70 00 20 00 00 00 00 00 00 00 00 00 6C 6F 61 64 20 66 72 6F 6D 20 6D 69 73 61 6C 69 67 6E 65 64 20 72 61 77 20 70 6F 69 6E 74 65 72 00 66 61 74 61 6C 20 65 72 72 6F 72 00 00 00 00 69 6E 76 61 6C 69 64 20 75 6E 73 61 66 65 44 6F 77 6E 63 61 73 74 00 00

B181CF188E162400 B181CF188E162400 680A81A610680A01 AAAAAAAAAAAAAA0A 0500000000000000 88982D1401000000 0000000000000000 C0922D1401000000 0000000000000000 C0922D1401000000 0000000000000000 7A00610070000030 7800200000000000 756E657870656374 65646C7920666F75 6E64206E696C2077 68696C6520756E77 72617070696E6720

B181CF188E162400 B181CF188E162400 680A81A610680A01 AAAAAAAAAAAAAA0A 0500000000000000 88982D1401000000 0000000000000000 C0922D1401000000 0000000000000000 C0922D1401000000 0000000000000000 7A00610070000030 7800200000000000 756E657870656374 65646C7920666F75 6E64206E696C2077 68696C6520756E77 72617070696E6720 0x9868 0x9870 0x9878 0x9880 0x9888 0x9890 0x9898 0x98A0 0x98A8 0x98B0 0x98B8 0x98C0 0x98C8 0x98D0 0x98D8 0x98E0 0x98E8 0x98F0

var age = 5 B181CF188E162400 B181CF188E162400 680A81A610680A01 AAAAAAAAAAAAAA0A 0500000000000000 88982D1401000000 0000000000000000 C0922D1401000000 0000000000000000 C0922D1401000000 0000000000000000 7A00610070000030 7800200000000000 756E657870656374 65646C7920666F75 6E64206E696C2077 68696C6520756E77 72617070696E6720 0x9868 0x9870 0x9878 0x9880 0x9888 0x9890 0x9898 0x98A0 0x98A8 0x98B0 0x98B8 0x98C0 0x98C8 0x98D0 0x98D8 0x98E0 0x98E8 0x98F0

B181CF188E162400 B181CF188E162400 680A81A610680A01 AAAAAAAAAAAAAA0A 0500000000000000 88982D1401000000 0000000000000000 C0922D1401000000 0000000000000000 C0922D1401000000 0000000000000000 7A00610070000030 7800200000000000 756E657870656374 65646C7920666F75 6E64206E696C2077 68696C6520756E77 72617070696E6720 0x9868 0x9870 0x9878 0x9880 0x9888 0x9890 0x9898 0x98A0 0x98A8 0x98B0 0x98B8 0x98C0 0x98C8 0x98D0 0x98D8 0x98E0 0x98E8 0x98F0 var age = 5

B181CF188E162400 B181CF188E162400 680A81A610680A01 AAAAAAAAAAAAAA0A 0500000000000000 0x9868 0x9870 0x9878 0x9880 0x9888 var age = 5 withUnsafePointer(to: &age) { // ... }

B181CF188E162400 B181CF188E162400 680A81A610680A01 AAAAAAAAAAAAAA0A 0500000000000000 0x9868 0x9870 0x9878 0x9880 0x9888 var age = 5 withUnsafePointer(to: &age) { agePointer in // ... }

B181CF188E162400 B181CF188E162400 680A81A610680A01 AAAAAAAAAAAAAA0A 0500000000000000 0x9868 0x9870 0x9878 0x9880 0x9888 var age = 5 withUnsafePointer(to: &age) { agePointer in print(agePointer.pointee) } > 5

Unsafe
 Pointer
 Types

UnsafePointer UnsafeMutablePointer UnsafeRawPointer UnsafeMutableRawPointer

UnsafePointer UnsafeMutablePointer UnsafeRawPointer UnsafeMutableRawPointer Typed

UnsafePointer UnsafeMutablePointer UnsafeRawPointer UnsafeMutableRawPointer B181CF188E162400 B181CF188E162400 680A81A610680A01 AAAAAAAAAAAAAA0A 0500000000000000 88982D1401000000 0000000000000000 C0922D1401000000 0000000000000000 C0922D1401000000 0000000000000000 7A00610070000030 7800200000000000 756E657870656374 65646C7920666F75 6E64206E696C2077 68696C6520756E77 72617070696E6720 0x9868 0x9870 0x9878 0x9880 0x9888 0x9890 0x9898 0x98A0 0x98A8 0x98B0 0x98B8 0x98C0 0x98C8 0x98D0 0x98D8 0x98E0 0x98E8 0x98F0

UnsafePointer UnsafeMutablePointer UnsafeRawPointer UnsafeMutableRawPointer Raw

UnsafePointer UnsafeMutablePointer UnsafeRawPointer UnsafeMutableRawPointer

UnsafeMutablePointer UnsafeMutableRawPointer UnsafePointer UnsafeRawPointer Immutable

UnsafeMutablePointer UnsafeMutableRawPointer Mutable

B181CF188E162400 B181CF188E162400 680A81A610680A01 AAAAAAAAAAAAAA0A 0500000000000000 0x9868 0x9870 0x9878 0x9880 0x9888 var age = 5 withUnsafeBytes(of: &age) { // ... }

B181CF188E162400 B181CF188E162400 680A81A610680A01 AAAAAAAAAAAAAA0A 0500000000000000 0x9868 0x9870 0x9878 0x9880 0x9888 var age = 5 withUnsafeBytes(of: &age) { ageBytes in ageBytes.count // 8 ageBytes.first // Optional(5) ageBytes[0] // 5 }

var age = 2000 withUnsafeBytes(of: &age) { ageBytes in ageBytes.count // 8 ageBytes.first // Optional(208) ageBytes[0] // 208 } B181CF188E162400 B181CF188E162400 680A81A610680A01 AAAAAAAAAAAAAA0A D007000000000000 0x9868 0x9870 0x9878 0x9880 0x9888

Imported C APIs Speed

func SKSearchFindMatches( _ inMaximumCount: CFIndex, _ outIDsArray: UnsafeMutablePointer!, _ outFoundCount: UnsafeMutablePointer! ) -> Bool

let limit = 100 var foundCount = 0 as CFIndex var documentIDs = Array(repeating: 0 as SKDocumentID, count: limit) _ = SKSearchFindMatches(CFIndex(limit), &documentIDs, &foundCount) for i in 0..

let limit = 100 var foundCount = 0 as CFIndex var documentIDs = Array(repeating: 0 as SKDocumentID, count: limit) _ = SKSearchFindMatches(CFIndex(limit), &documentIDs, &foundCount) for i in 0..

let limit = 100 var foundCount = 0 as CFIndex var documentIDs: [SKDocumentID] = [] documentIDs.reserveCapacity(limit) _ = SKSearchFindMatches(CFIndex(limit), &documentIDs, &foundCount) for i in 0..

let limit = 100 var foundCount = 0 as CFIndex var documentIDs = Array(repeating: 0 as SKDocumentID, count: limit) _ = SKSearchFindMatches(CFIndex(limit), &documentIDs, &foundCount) for i in 0..

let limit = 100 var foundCount = 0 as CFIndex let documentIDs = UnsafeMutablePointer .allocate(capacity: limit) defer { documentIDs.deallocate(capacity: limit) } _ = SKSearchFindMatches(CFIndex(limit), documentIDs, &foundCount) for i in 0..

let limit = 100 var foundCount = 0 as CFIndex let documentIDs = UnsafeMutablePointer .allocate(capacity: limit) defer { documentIDs.deallocate(capacity: limit) } _ = SKSearchFindMatches(CFIndex(limit), documentIDs, &foundCount) for i in 0..

func bubbleSort(_ array: inout [T]) { guard !array.isEmpty else { return } for n in 1.. array[i] { swap(&array[i - 1], &array[i]) } } } }

func bubbleSort(_ array: inout [T]) { guard !array.isEmpty else { return } array.withUnsafeMutableBufferPointer { buffer in for n in 1.. buffer[i] { swap(&buffer[i - 1], &buffer[i]) } } } } }

Really Not Safe at All

var age = 2000 let agePointer = UnsafeMutablePointer(&age) agePointer.pointee = 10 // age == 10

var age = 2000 let agePointer = withUnsafeMutablePointer(to: &age) { p in return p } agePointer.pointee = 10 // age == 10

var age = 2000 let agePointer = UnsafeMutablePointer(&age) agePointer.pointee = 10 // age == 10 undefined
 behavior

Swift’s Pointy Bits Nate Cook @nnnnnnnn