Swift compare memory addresses

Question

I want to compare the addresses of two Swift objects, like:

let a: AnyObject
let b: AnyObject

a < b

Of course this is not possible like this but I’m not able to find any way to achieve this.

I could just implement a C function to do this

bool compare(NSObject *a, NSObject *b){
    return a < b;
}

and then call it like

compare(a, b)

but this limits me to use NSObjects.

So my question is: Is there any way to achieve this purely in Swift?

score 5 · Accepted Answer · edited Aug 29 '15 at 13:33

5

You can use the unsafeAddressOf function that returns an UnsafePointer value.

let elm0 = "hello world"
let elm1 = UIButton()

let address0 = unsafeAddressOf(elm0)
let address1 = unsafeAddressOf(elm1)

let compare = address0 > address1

Hope this helps.

edited Aug 29 '15 at 13:33

Sulthan

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answered Aug 29 '15 at 13:16

Luca Angeletti

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Exactly what I was looking for, much better than my own solution. Where is this documented? I was not able to find any function like this. – idmean Aug 29 '15 at 13:18
Yes, but how did you find that function? I don’t want to ask a question every time I'm looking for such a global function. – idmean Aug 29 '15 at 13:22
http://stackoverflow.com/questions/24058906/printing-a-variable-memory-address-in-swift – Luca Angeletti Aug 29 '15 at 13:23
Ok, deep searching on Stack Overflow. Sadly Swift lacks documentation. Thanks for your help. – idmean Aug 29 '15 at 13:24
1

I have added a link to Apple documentation (prerelease, the link will have to be updated later). – Sulthan Aug 29 '15 at 13:34
1

@LucaAngeletti the documentation link does not exist anymore. – Surjeet Rajput Feb 28 '21 at 09:09

score 3 · Answer 2 · answered Aug 29 '15 at 13:16

I found myself an answer.

There is a struct called ObjectIdentifier which can provide you a UIntValue to identify an object.

This UIntValue looks pretty much like it was the object reference, so I’ll use that:

class Person {
    var name: String

    init(name: String){
        self.name = name
    }
}

NSLog("%p", ObjectIdentifier(Person(name: "James")).uintValue)
NSLog("%p", ObjectIdentifier(Person(name: "Berta")).uintValue)
NSLog("%p", ObjectIdentifier(Person(name: "Charly")).uintValue)

Logs something similar to:

2015-08-29 15:04:21.567 App[10724:5283560] 0x7ff3a8415830
2015-08-29 15:04:21.568 App[10724:5283560] 0x7ff3a8643ba0
2015-08-29 15:04:21.568 App[10724:5283560] 0x7ff3a8415830

Swift compare memory addresses

2 Answers2