mach - Swift pointer problems with MACH_TASK_BASIC_INFO

Question

I am trying to convert an ObjC stackoverflow answer to Swift and failing. It looks like I am passing a UnsafeMutablePointer<mach_msg_type_number_t> when I should be passing an inout mach_msg_type_number_t and I can't seem to work out my problem. From what I understand of the Swift pointer documentation (not much) these should be interchangeable..?

Further info below.

Here's the Objective C:

struct task_basic_info info;
mach_msg_type_number_t size = sizeof(info);
kern_return_t kerr = task_info(mach_task_self(), TASK_BASIC_INFO, (task_info_t)&info, &size);

and here's as far as I got in Swift (many lines for easier type checking)

let name: task_name_t = mach_task_self_
let flavor: task_flavor_t = task_flavor_t(MACH_TASK_BASIC_INFO)
var info: mach_task_basic_info
var size: mach_msg_type_number_t = UnsignedFixed(sizeof(mach_task_basic_info_t))
let kerr = task_info(name, flavor, info as task_info_t, &size)

The task_info signature is:

func task_info(target_task: task_name_t, flavor: task_flavor_t, task_info_out: task_info_t, task_info_outCnt: UnsafeMutablePointer<mach_msg_type_number_t>) -> kern_return_t

and the error on the last line is:

Cannot convert the expression's type '(@!lvalue task_name_t, task_flavor_t, task_info_t, inout mach_msg_type_number_t)' to type 'kern_return_t'

Answer 1

Took me a bit to update Airspeed Velocity's answer to the latest swift syntax (Swift 3, beta 6), but here is what I got:

func report_memory() {
    var info = mach_task_basic_info()
    let MACH_TASK_BASIC_INFO_COUNT = MemoryLayout<mach_task_basic_info>.stride/MemoryLayout<natural_t>.stride
    var count = mach_msg_type_number_t(MACH_TASK_BASIC_INFO_COUNT)

    let kerr: kern_return_t = withUnsafeMutablePointer(to: &info) {
        $0.withMemoryRebound(to: integer_t.self, capacity: MACH_TASK_BASIC_INFO_COUNT) {
            task_info(mach_task_self_,
                      task_flavor_t(MACH_TASK_BASIC_INFO),
                      $0,
                      &count)
        }
    }

    if kerr == KERN_SUCCESS {
        print("Memory in use (in bytes): (info.resident_size)")
    }
    else {
        print("Error with task_info(): " +
            (String(cString: mach_error_string(kerr), encoding: String.Encoding.ascii) ?? "unknown error"))
    }
}

Hope that's helpful.