> In order to evaluate this more fully, I'd like to see some examples of real
> code that would be improved by having this facility, but in general, I'd be
> concerned that this proposal making mutating/side-effectful method calls look
> more like purely-functional ones.
Mh, maybe I'm a little bit old-fashioned, but I expect side effects everywhere
unless purity is guaranteed ;-)
It's really no big thing - one example is small enough to inline it instead of
pushing a playground.
As Kevin pointed out, there are solutions that are probably better, but require
a real change in the language.
I think Objective-C didn't copy the chaining-pattern from Smalltalk because
it's quite ugly to calculate the number of opening braces in advance, but in
Swift, I really like that approach.
Builders are actually the most common use case, but the pattern fits well
wherever you have to do configuration.
Of cause, it's always a bit of personal preference how to rate a solution, but
for those who like the concept of fluent interfaces, returning self is much
more valuable than void (well, considering the traffic, it doesn't seem that
many Swift-Users care for the topic ;-).
import Cocoa
func backgroundStuff() {
print("Working very hard...")
NSThread.sleepForTimeInterval(0.5)
}
func finish() {
print("Just imagine I'm doing some GUI-cleanup")
}
func current() {
let queue = NSOperationQueue()
let mainOperation = NSBlockOperation(block: backgroundStuff)
mainOperation.name = "Download-Task"
mainOperation.queuePriority = .VeryHigh
queue.addOperation(mainOperation)
let cleanup = NSBlockOperation(block: finish)
cleanup.queuePriority = .Low
cleanup.addDependency(mainOperation)
NSOperationQueue.mainQueue().addOperation(cleanup)
}
extension NSOperation {
func addToQueue(queue: NSOperationQueue = NSOperationQueue.mainQueue())
-> Self {
queue.addOperation(self)
return self
}
func changePriority(priority: NSOperationQueuePriority = .Normal) ->
Self {
queuePriority = priority
return self
}
func changeName(name: String) -> Self {
self.name = name
return self
}
func waitFor(dependency: NSOperation) -> Self {
addDependency(dependency)
return self
}
}
func fluent() {
let queue = NSOperationQueue()
let mainOperation = NSBlockOperation(block:
backgroundStuff).changeName("DownloadTask").changePriority(.VeryHigh)
mainOperation.addToQueue(queue)
NSBlockOperation(block:
finish).changePriority(.Low).waitFor(mainOperation).addToQueue()
}
// second one - this wont actually compile, but the needed code wouldn't be
complicated
self.view.layer.changeBorderWidth(3).changeBorderColor(UIColor.redColor().CGColor)
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