[swift-users] Making a copy of an UnsafePointer<UInt8>

Quinn "The Eskimo!" eskimo1 at apple.com
Wed Nov 15 02:48:22 CST 2017

On 15 Nov 2017, at 04:16, Rick Mann via swift-users <swift-users at swift.org> wrote:

> Is UnsafeMutablePointer<> not memory managed?

It is not.  Specifically, the code you posted creates a copy of the data and then never destroys it.

If I were in your shoes I’d construct a `Data` value from the unsafe pointer and then pass that around.

let source = Data(bytes: inSourceBuffer, count: inSourceBufferLength)
self.queue.async {
    let size = source.count
    source.withUnsafeBytes { (p: UnsafePointer<UInt8>) in
        self.foo(data: p, length: size)

The main drawback to this is that you have to jump through the hoops to access the data unsafely.  It might be easier to recast your consumer (the `foo(…)` method) in terms of `Data`.  That’s what I generally do when I work with foreign APIs like this, that is, keep the data in ‘Swift space’ and only deal with foreign types at the boundaries.

Whether that makes sense here really depends on the specifics of your program.  For example, if your program has lots of this boundary code, it might be nicer to just stick with the foreign type.  Or build a specific wrapper that makes it easier to do this conversion.

Share and Enjoy
Quinn "The Eskimo!"                    <http://www.apple.com/developer/>
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

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