[swift-users] How to malloc in Swift 3

Gerriet M. Denkmann gerrietm at me.com
Sat Sep 24 22:36:23 CDT 2016

> On 23 Sep 2016, at 19:41, Quinn The Eskimo! via swift-users <swift-users at swift.org> wrote:
> On 23 Sep 2016, at 11:29, Gerriet M. Denkmann via swift-users <swift-users at swift.org> wrote:
>> What about calloc then? Or use allocate and do a memset afterwards?
> For trivial data types (like UInt8) this will work, but if you want to follow the rules I recommend reading the following:
> * UnsafeRawPointer Migration
> <https://swift.org/migration-guide/se-0107-migrate.html>
> * SE-0107 “UnsafeRawPointer API”
> <https://github.com/apple/swift-evolution/blob/master/proposals/0107-unsaferawpointer.md>
> Spoiler: that’ll point you to `initialize(to:count:)` (-:

Thanks for the links.
By the way: I had already tried to use `initialize(to:count:)` before, but I used it as a replacement of allocate, which the compiler did not really like.
Since reading these documents I know that I have to use it after allocate, not instead of.

In dealloc I had before:
	free( bitfield )
which, to my surprise, the compiler did NOT warn about (should there be a warning?)
I have since replace this with:
	bitfield.deallocate(capacity: numberUsedInAllocate )

>                   *                   *                   *
> Also, why are you manually allocating this rather than using [UInt8]?  The latter is easier, safer, and likely to have similar levels of efficiency.

I just tried this:  [UInt8] turns out to be nearly 10% slower compared to: UnsafeMutablePointer<UInt8>.allocate(capacity:).

Probably depends on the use case, whether 10% less performance is worth the easier and safer.
I am trying to compare Swift to ObjC classes (which use malloc), so it would not be a fair comparison if the Swift class has to use an UInt8 array.

Kind regards,


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