Thanks a lot Andrew and Quinn,
After your explanation, I understand the following better now:
- It makes sense to get the memory address of a reference type as it represents
identity. Just realised there is also === identity operator to check if it is
the same reference.
- The need to get the memory address of a value type might not be of the same
significance (as it is a value) and the emphasis would be more on the equality
of the value.
- And model based on whether the entity represents identity / value
Thanks and regards,
Muthu
> On 13 Sep 2017, at 1:19 AM, Andrew Trick <atr...@apple.com> wrote:
>
>>
>> On Sep 12, 2017, at 9:55 AM, somu subscribe via swift-users
>> <swift-users@swift.org> wrote:
>>
>> Hi Quinn,
>>
>> Thanks for the reply,
>>
>> It is an iOS Swift project (uses Foundation, UIKit, CloudKit and other
>> native frameworks) in which I would like to check the memory address for
>> debugging (and out of enthusiasm). There is no C code I am using.
>>
>> I have some asynchronous call back functions from CloudKit frameworks which
>> return CKUserIdentity objects.
>>
>> So thought it would be nice if I could print the memory address of
>> CKUserIdentity objects and to check if it was unique.
>>
>> And there are some other custom Swift Structs which I would like to know the
>> memory address of.
>>
>> Thanks and regards,
>> Muthu
>
> For classes, use the Unmanaged API as Quinn’s suggested.
>
> Your structs, tuples, and enums only have an address during mutation. So, for
> example, if you wrap all of your code in a function that takes the variable
> `inout`, you’ll see a consistent address within a single call to that
> function. There’s an implicit cast from `inout` to Unsafe[Mutable]Pointer
> arguments, so you can inspect the pointer value...
>
> func foo(p: Unsafe[Mutable]Pointer) { print(p) }
>
> foo(&s2)
>
> As you noticed, between calls to `foo` you could see a different address.
>
> If you really want to give your structs an “identity” you would need to wrap
> them in a class.
>
> -Andy
>
>>> On 12 Sep 2017, at 10:35 PM, Quinn The Eskimo! via swift-users
>>> <swift-users@swift.org> wrote:
>>>
>>>
>>> On 12 Sep 2017, at 13:44, somu subscribe via swift-users
>>> <swift-users@swift.org> wrote:
>>>
>>>> 1. Is the above shown the correct way to get reference type memory address
>>>> ?
>>>> 2. What Is it the correct way to get value type memory address ?
>>>
>>> It’s hard to answer that without knowing how you’re intended to use these
>>> techniques. If you can explain more about where you’re going with this, I
>>> should be able to make some specific recommendations.
>>>
>>> For example, if you’re goal were to pass a Swift object to a C API that
>>> takes a callback function pointer and a ‘cookie’ value, and hen calls that
>>> function with that cookie (like the `qsort_r` function), the to/from opaque
>>> mechanism provider by `Unmanaged` is the recommended way to pass a Swift
>>> object through such a cookie value.
>>>
>>>> 3. Is it possible to get the memory address of immutable value type
>>>> (declared as let)
>>>
>>> No, because such values don’t necessarily exist in memory.
>>>
>>> Share and Enjoy
>>> --
>>> Quinn "The Eskimo!" <http://www.apple.com/developer/>
>>> Apple Developer Relations, Developer Technical Support, Core OS/Hardware
>>>
>>>
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