I know were you are coming from, but:
1. In other languages it would be the equivalent of an force unwrapped
optional and you could get a NullPointerException (or worse - core dump).
Using a force unwrapped optional just levels the playing field!
2. You could make it private(set) which would de-risk the var bit.
3. See below.
class AssignOnce<T: AnyObject> {
weak var value: T? = nil { // Use a weak var to avoid a retain cycle.
willSet {
guard value == nil else {
fatalError("Can only be set once.")
}
}
}
}
class InitSelfDependency {
let dependsUponSelf = AssignOnce<InitSelfDependency>()
init() {
dependsUponSelf.value = self
}
}
let i = InitSelfDependency()
i.dependsUponSelf
On Tue, 26 Sep 2017 at 4:44 pm, Kenny Leung via swift-users <
swift-users@swift.org> wrote:
> Hi Howard.
>
> Yes, this would make it compile, but it still would not solve the issues
> that make it wrong in my mind:
>
> 1. I would have to make it a var, but it should not be mutable.
>
> 2. It’s not optional. Without it, the PDAudioPlayer class could not
> function.
>
> Of course, this is just being stubbornly pedantic about the code, but the
> whole point of this project is an exercise in pedantry.
>
> -Kenny
>
>
> On Sep 25, 2017, at 10:35 PM, Howard Lovatt <howard.lov...@gmail.com>
> wrote:
>
> You could try making mQueue a force unwrapped optional or initialize it to
> a failed queue before overwriting on last line of `init`.
>
> On Tue, 26 Sep 2017 at 11:39 am, Kenny Leung via swift-users <
> swift-users@swift.org> wrote:
>
>> Hi Muthu.
>>
>> Thanks for the suggestion.
>>
>> I don’t want to do that because failure to create the AudioQueue should
>> mean failure to create the AudioPlayer itself.
>>
>> -Kenny
>>
>>
>> On Sep 25, 2017, at 6:33 PM, somu subscribe <somu.subscr...@gmail.com>
>> wrote:
>>
>> Hi Kenny,
>>
>> You could use a lazy var and initialise it with a closure.
>>
>> class PDAudioPlayer {
>>
>> //Would be created lazily when first invoked
>> lazy var mQueue : AudioQueueRef = {
>>
>> //create an audioQueue and return that instance
>> return audioQueue
>> }()
>> }
>>
>> Thanks and regards,
>> Muthu
>>
>>
>> On 26 Sep 2017, at 9:12 AM, Kenny Leung via swift-users <
>> swift-users@swift.org> wrote:
>>
>> Hi All.
>>
>> I’m trying to implement the AudioQueue example from Apple in Swift, and
>> keep it as Swifty as I can. I’ve run into a problem where I have a let ivar
>> for the AudioQueue, but the only way to initialize that let ivar is to pass
>> a block to the function that creates the AudioQueue. I get the error,
>> "Variable 'self.mQueue' used before being initialized”. Is there any way to
>> get around this catch?
>>
>> Thanks!
>>
>> -Kenny
>>
>> The code follows.
>>
>> ———8<————8<————
>> class PDAudioPlayer {
>> static let kNumberBuffers :Int = 3 // 1
>> //var mDataFormat:AudioStreamBasicDescription //
>> 2
>> let mQueue :AudioQueueRef // 3
>> //var mBuffers :[AudioQueueBufferRef] // 4
>> //var mAudioFile :AudioFileID? //
>> 5
>> var bufferByteSize :UInt32? // 6
>> var mCurrentPacket :Int64? // 7
>> var mNumPacketsToRead :UInt32? // 8
>> var mPacketDescs :UnsafePointer<AudioStreamPacketDescription>? // 9
>> var mIsRunning: Bool = false // 10
>>
>> let dispatchQueue :DispatchQueue
>> let source :PDFileAudioSource
>> var audioBuffers :[PDAudioBuffer]
>>
>> init?(source:PDFileAudioSource) {
>> self.source = source
>> self.dispatchQueue = DispatchQueue(label:"AudioPlayer", qos:.
>> default, attributes:[], autoreleaseFrequency:.workItem, target:nil)
>> self.audioBuffers = [PDAudioBuffer]()
>>
>> var tempAudioQueue :AudioQueueRef?
>> var dataFormat = source.mDataFormat
>> let status = AudioQueueNewOutputWithDispatchQueue(&tempAudioQueue,
>> &dataFormat, 0, self.dispatchQueue) { [weak self] (queue, buffer) in
>> // ERROR on this line
>> guard let this = self else {
>> return // block
>> }
>> guard let audioBuffer =
>> this.audioBufferForAudioQueueBuffer(aqBuffer:buffer)
>> else {
>> return // block
>> }
>> this.source.fillBuffer(audioBuffer)
>> }
>> if status != 0 {
>> return nil
>> }
>> guard let audioQueue = tempAudioQueue else {
>> return nil
>> }
>> self.mQueue = audioQueue
>> }
>>
>> private func audioBufferForAudioQueueBuffer(aqBuffer:
>> AudioQueueBufferRef) -> PDAudioBuffer? {
>> for buffer in self.audioBuffers {
>> if buffer.audioQueueBuffer == aqBuffer {
>> return buffer
>> }
>> }
>> return nil
>> }
>> }
>>
>> _______________________________________________
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>> swift-users@swift.org
>> https://lists.swift.org/mailman/listinfo/swift-users
>>
>>
>>
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>>
> --
> -- Howard.
>
>
> _______________________________________________
> swift-users mailing list
> swift-users@swift.org
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>
--
-- Howard.
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