Generic Enumeration

MemoryLayout

The memory layout of a type, describing its size, stride, and alignment.

Overview

You can use MemoryLayout as a source of information about a type when allocating or binding memory using unsafe pointers. The following example declares a Point type with x and y coordinates and a Boolean isFilled property.

struct Point {
    let x: Double
    let y: Double
    let isFilled: Bool
}

The size, stride, and alignment of the Point type are accessible as static properties of MemoryLayout<Point>.

// MemoryLayout<Point>.size == 17
// MemoryLayout<Point>.stride == 24
// MemoryLayout<Point>.alignment == 8

Always use a multiple of a type’s stride instead of its size when allocating memory or accounting for the distance between instances in memory. This example allocates untyped, uninitialized memory with space for four instances of Point.

let count = 4
let pointPointer = UnsafeMutableRawPointer.allocate(
        bytes: count * MemoryLayout<Point>.stride,
        alignedTo: MemoryLayout<Point>.alignment)

Topics

Type Properties

static var alignment: Int

The default memory alignment of T, in bytes.

static var size: Int

The contiguous memory footprint of T, in bytes.

static var stride: Int

The number of bytes from the start of one instance of T to the start of the next when stored in contiguous memory or in an Array<T>.

Type Methods

static func alignment(ofValue: T)

Returns the default memory alignment of T.

static func size(ofValue: T)

Returns the contiguous memory footprint of the given instance.

static func stride(ofValue: T)

Returns the number of bytes from the start of one instance of T to the start of the next when stored in contiguous memory or in an Array<T>.