[swift-users] EnumerateUsingObjects in Swift

[Zhao Xin]

It seems to me that you didn't initialize your `myArray` before you casted
it. That caused the problem.

Zhaoxin

On Tue, Jan 24, 2017 at 9:34 AM, Jon Shier via swift-users <
swift-users at swift.org> 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> 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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