escapeanaemia / swift-memorylayout

Swift MemoryLayout Description

Swift MemoryLayout

swift version =>: swift 5.0

• Swift
  • Struct
  • Tuple
  • Class
  • Protocol
  • Enum
• SwiftCore
  • Bool
  • Optional
  • String
  • Character
  • Array
  • Set
  • Dictionary

Swift

Struct

struct StructValue {
    let a: Int8 = 4
    let b: Int16 = 6
    let c: Int32 = 8
}

var structValue = StructValue()
let structValuePointer = withUnsafePointer(to: &structValue) { UnsafeMutableRawPointer(mutating: $0) }
structValuePointer.advanced(by: 2).assumingMemoryBound(to: Int16.self).initialize(to: 99)

// structValue.b = 99

Tuple

typealias TupleValue = (Int8, Int32, String)

struct StructValue {
    var a: Int8 = 4
    var b: Int32 = 5
    var c: String = "SwiftTuple"
}

let structValue = StructValue()
let tupleValue = unsafeBitCast(structValue, to: TupleValue.self)
print(tupleValue.1)

// print 5    (structValue.b)

// if TupleValue = (Int8, Int8, String) =>  MemoryLayout of TupleValue !=  MemoryLayout of StructValue

Class

class A {
    var a = 666
}

let a1 = A()
unowned let unowned_a = a1
let a2 = a1

weak var weak_a = a1
weak var weak_a2 = a1

unowned let unowned_a2 = a1

let a3 = a2
let a4 = a2
weak var weak_a3 = a1
unowned let unowned_a3 = a1

print(UnownedRefCount(a1))
print(WeakRefCount(a1)!)
print(StrongRefCount(a2))

Protocol

// test with debug 
protocol SwiftProtocol {
    func foo()
    func foo2()
}

struct StructValue: SwiftProtocol {
    func foo() {
        print("foo")
    }
    
    func foo2() {
        print("foo2")
    }
}

var Protocol: SwiftProtocol = StructValue()
let protocol_pointer = withUnsafePointer(to: &Protocol) { UnsafeMutableRawPointer(mutating: $0) }

let witness_table_pointer_value = protocol_pointer.advanced(by: 32).assumingMemoryBound(to: UInt.self).pointee
let witness_table_pointer = UnsafeMutablePointer<UnsafeMutableRawPointer>.init(bitPattern: witness_table_pointer_value)

typealias Foo2Method = @convention(thin) ()->Void 

let witness_foo2_pointer = unsafeBitCast(witness_table_pointer!.advanced(by: 2).pointee, to: Foo2Method.self)
witness_foo2_pointer()

// print foo2

Enum

enum EnumValue {
    case a
    case b(String)
    case c(Int32)
    case d
    case f(Int64)
    case e
}

var enumC = EnumValue.c(8)
let enumCPointer = withUnsafePointer(to: &enumC) { UnsafeMutableRawPointer(mutating: $0) }
enumCPointer.advanced(by: 16).assumingMemoryBound(to: Int8.self).initialize(to: 0x02)

// enumC = EnumValue.f(8)

SwiftCore

Bool

var bool = true
let boolPointer = bool.valuePointer
boolPointer.initialize(to: -10)

// bool = false 

Optional

var optional: Int16?      // 0x00 0x00 0x01
var optionalPointer = optional.valuePointer
optionalPointer.assumingMemoryBound(to: Int16.self).initialize(to: 99)  // 0x63 0x00 0x01
optionalPointer.advanced(by: MemoryLayout<Int16>.size).assumingMemoryBound(to: UInt8.self).initialize(to: 0x00)  // 0x63 0x00 0x00

// optional = 99

String

var string = "TannerJin"
let stringPointer = string.valuePointer
stringPointer.assumingMemoryBound(to: Int8.self).initialize(to: 0x40)      // 0x40 => "@"

// string = "@anner Jin"    

Character

var character = Character("😂")
let characterPointer = character.valuePointer.assumingMemoryBound(to: UInt8.self)
characterPointer.initialize(to: 0xf0)                             // f0 9f 9a 80 => "🚀"  unicode(utf-8)
characterPointer.advanced(by: 1).initialize(to: 0x9f)
characterPointer.advanced(by: 2).initialize(to: 0x9a)
characterPointer.advanced(by: 3).initialize(to: 0x80)

// character = "🚀"

Array

let array = ["Apple", "Swift"]
let arrayPointer = array.valuePointer
arrayPointer.initialize(to: "Tanner")

// array = ["Tanner", "Swift"]

array.countPointer.initialize(to: 3)

// array.count = 3

Set

let set: Set<String> = ["Apple", "iOS", "Swift"]
set.valuesPointer.initialize(to: "Tanner")

// set =  ["Tanner", "Swift", "iOS"] ||  ["Tanner", "Swift", "Apple"] || ...

set.countPointer.initialize(to: 2)

// set.count = 2

Dictionary

let dictionary = ["Swift": 5.0, "iOS": 2019]

let dicCountPointer = dictionary.countPointer
let dicKeysPointer = dictionary.keysPointer
let dicValuesPointer = dictionary.valuesPointer