[swift-users] EnumerateUsingObjects in Swift

[Doug Hill]

Thanks for the tip about 'concurrentPerform'!

> On Jan 23, 2017, at 5:34 PM, Jon Shier <jon at jonshier.com> wrote:
> 
> 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 <mailto: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
>> _______________________________________________
>> swift-users mailing list
>> swift-users at swift.org <mailto:swift-users at swift.org>
>> https://lists.swift.org/mailman/listinfo/swift-users
> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-users/attachments/20170125/d35dd82e/attachment.html>