Calls a closure with a pointer to the array’s contiguous storage.
SDK
- Xcode 10.0+
Framework
- Swift Standard Library
Declaration
func withUnsafeBufferPointer<R>(_ body: (UnsafeParameters
bodyA closure with an
Unsafeparameter that points to the contiguous storage for the array. If no such storage exists, it is created. IfBuffer Pointer bodyhas a return value, that value is also used as the return value for thewithmethod. The pointer argument is valid only for the duration of the method’s execution.Unsafe Buffer Pointer(_:)
Return Value
The return value, if any, of the body closure parameter.
Discussion
Often, the optimizer can eliminate bounds checks within an array algorithm, but when that fails, invoking the same algorithm on the buffer pointer passed into your closure lets you trade safety for speed.
The following example shows how you can iterate over the contents of the buffer pointer:
let numbers = [1, 2, 3, 4, 5]
let sum = numbers.withUnsafeBufferPointer { buffer -> Int in
var result = 0
for i in stride(from: buffer.startIndex, to: buffer.endIndex, by: 2) {
result += buffer[i]
}
return result
}
// 'sum' == 9
The pointer passed as an argument to body is valid only during the execution of with. Do not store or return the pointer for later use.