[swift-users] EnumerateUsingObjects in Swift

[Jon Shier]

enumerateObjects(options:using:) exists on NSArray in Swift. And I was able to create your generic class just fine:

class Test<T> {
    var array: [T] = []
    
    init() {
        var temp = array as NSArray
    }
}

I’m not sure what the canonical parallel array enumeration would be, but you can do it using concurrentPerform:

let array = [“one”, “two”]
DispatchQueue.concurrentPerform(iterations: array.count) { index in
    print(array[index])
}


> On Jan 23, 2017, at 8:20 PM, Doug Hill via swift-users <swift-users at swift.org> wrote:
> 
> I'm trying to accomplish the equivalent functionality of -[NSArray enumerateUsingObjects:…] in Swift. Doing a Googles search, I see that one would need to call the equivalent method on the bridged NSArray version of your Swift array:
> 
> var myNSArray : NSArray = mySwiftArray as NSArray
> 
> Here's the problem I'm running into; I have the following class:
> 
> class Tester<typeA>
> {
> 	var myArray : [typeA]
> 
> 	init()
> 	{
> 		var temp = self. myArray as NSArray
> 	}
> }
> 
> Which produces a compiler error:
> 
> 'cannot convert value of type '[typeA]' to type 'NSArray' in coercion'
> 
> Ok, this makes some sense since I'm guessing NSArray requires each element to to be an NSObject but this array type Array<typeA> could be a non-NSObject.
> 
> However, this makes my code harder to write since I now have to make sure any array has element type NSObject to use enumerateUsingObjects. Not something I can either guarantee or even desire.
> 
> The reason I like enumerateUsingObjects is that it supports a functional style of programming and is better at creating work items for each object by dispatching each array item on multiple cores/processors/threads for me. Writing this method myself would require figuring out to pass an object to a dispatch invocation. But looking through the swift API's, I don't see any GCD method for passing an object to dispatch_sync/async. I see versions of these methods that takes a context parameter but then takes a C function instead of a block, so not very Swift-like and potentially unsafe.
> 
> Does this mean enumerateUsingObjects is generally not all that useful in Swift? Are there better alternatives? Any ideas on how best to handle this situation would be appreciated.
> 
> Doug Hill
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