[swift-users] Object size on heap

Kate Stone k8stone at apple.com
Wed Mar 23 18:39:27 CDT 2016

I definitely concur that tools like Instruments are the best way to understand the impact of decisions on memory across the board.  For fine-grained inquiries about memory use you can also rely on malloc family functions to make inquiries:

let required_size = malloc_size(unsafeAddressOf(object_reference))
let actual_size = malloc_good_size(required_size)

Kate Stone k8stone at apple.com <mailto:k8stone at apple.com>
 Xcode Low Level Tools

> On Mar 23, 2016, at 3:59 PM, Howard Lovatt via swift-users <swift-users at swift.org> wrote:
> Thanks, I will give that a try
>   -- Howard.
> On 24 March 2016 at 03:17, Jens Alfke <jens at mooseyard.com <mailto:jens at mooseyard.com>> wrote:
>> On Mar 22, 2016, at 11:04 PM, Howard Lovatt via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
>> I am writing custom collection classes and trying to assess which one is better, both in terms of performance and memory usage. Won't be used in 'real' code, just to guide development.
> You might consider using heap profiling tools too, like (on Mac OS) the Instruments app or the `heap` command-line tool. If you use these while running a benchmark app using your API, it can show you how much total heap space gets used.
> Actual heap usage can differ from the raw “sizeof” a data type, since allocators will often round up block sizes or return a somewhat larger block than necessary. Heap fragmentation can also increase memory usage beyond what you’d expect, and different allocation patterns can affect fragmentation.
> —Jens
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