Generic Instance Method


Calls the given closure with a pointer to the underlying bytes of the array’s contiguous storage.


func withUnsafeBytes<R>(_ body: (UnsafeRawBufferPointer) throws -> R) rethrows -> R



A closure with an UnsafeRawBufferPointer parameter that points to the contiguous storage for the array. If no such storage exists, it is created. If body has a return value, that value is also used as the return value for the withUnsafeBytes(_:) method. The argument is valid only for the duration of the closure’s execution.

Return Value

The return value, if any, of the body closure parameter.


The array’s Element type must be a trivial type, which can be copied with just a bit-for-bit copy without any indirection or reference-counting operations. Generally, native Swift types that do not contain strong or weak references are trivial, as are imported C structs and enums.

The following example copies the bytes of the numbers array into a buffer of UInt8:

var numbers = [1, 2, 3]
var byteBuffer: [UInt8] = []
numbers.withUnsafeBytes {
    byteBuffer.append(contentsOf: $0)
// byteBuffer == [1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, ...]

See Also

Accessing Underlying Storage