UnsafePointer와 UnsafeMutablePointer

Swift의 형식 지정 pointer

// A pointer to an Int we can read but not write
func readFirst(_ p: UnsafePointer<Int>) -> Int {
    return p.pointee
}

포인터가 가리키는 값 속성

let p = UnsafeMutablePointer<Int>.allocate(capacity: 1)
p.initialize(to: 42)
print(p.pointee)   // 42
p.pointee = 99
print(p.pointee)   // 99

메모리 할당하기

// Reserve space for 3 Doubles (uninitialized)
let buffer = UnsafeMutablePointer<Double>.allocate(capacity: 3)
// Must initialize before reading any element

initialize와 deinitialize

let p = UnsafeMutablePointer<String>.allocate(capacity: 1)
p.initialize(to: "hello")
print(p.pointee)
p.deinitialize(count: 1) // releases the String
p.deallocate()

allocate와 deallocate는 항상 함께 사용하기

func process() {
    let p = UnsafeMutablePointer<Int>.allocate(capacity: 1)
    defer { p.deallocate() }
    p.initialize(to: 7)
    print(p.pointee)
} // deallocate runs here automatically

pointer 산술 연산

let p = UnsafeMutablePointer<Int>.allocate(capacity: 3)
p.initialize(repeating: 0, count: 3)
p[0] = 10
p[1] = 20
p[2] = 30
print((p + 1).pointee) // 20
p.deinitialize(count: 3)
p.deallocate()

여러 요소 initialize하기

let dst = UnsafeMutablePointer<Int>.allocate(capacity: 4)
dst.initialize(repeating: 5, count: 4)
print(dst[3]) // 5
dst.deinitialize(count: 4)
dst.deallocate()

읽기 전용 pointer와 가변 pointer 비교

func sum(_ p: UnsafePointer<Int>, _ n: Int) -> Int {
    var total = 0
    for i in 0..<n { total += p[i] }
    return total
}
// A mutable pointer can be passed here directly

로컬 값에 withUnsafePointer 사용하기

var value = 100
withUnsafeMutablePointer(to: &value) { ptr in
    ptr.pointee += 1
}
print(value) // 101

흔한 함정

// DANGEROUS — pointer escapes the closure
// var escaped: UnsafePointer<Int>?
// withUnsafePointer(to: &x) { escaped = $0 }
// escaped!.pointee  // dangling, undefined behavior

작은 수동 stack

let n = 3
let stack = UnsafeMutablePointer<Int>.allocate(capacity: n)
stack.initialize(repeating: 0, count: n)
for i in 0..<n { stack[i] = i * i }
// stack now holds 0, 1, 4
stack.deinitialize(count: n)
stack.deallocate()

빠른 확인

요약