That’s a nice one, Erica.
Does this mean there’s nothing ready-made for this in the standard library?
P.S. No need for the builder dictionary. A simple static function (T->U) would
be more enough for my use-case.
R+
> On 28 Dec 2015, at 20:26, Erica Sadun <er...@ericasadun.com> wrote:
>
> Maybe something like this?
>
> struct KeyedLazyCache<T: Hashable, U> {
> var backingDictionary: Dictionary<T, U>
> var builderDictionary: Dictionary<T, () -> U>
> mutating func clear() {backingDictionary.removeAll()}
> mutating func valueForKey(key: T) -> U? {
> if let value = backingDictionary[key] {return value}
> if let builder = builderDictionary[key] {
> let value = builder()
> backingDictionary[key] = value
> return value
> }
> return nil
> }
> }
>
> -- E
>
>> On Dec 28, 2015, at 11:36 AM, Rudolf Adamkovič via swift-users
>> <swift-users@swift.org <mailto:swift-users@swift.org>> wrote:
>>
>> Hi there!
>>
>> In my app, I have a very simple class that serves as a key-value cache. The
>> whole thing is basically a lazily populated [String: AVAudioPCMBuffer]
>> dictionary with a String -> AVAudioPCMBuffer function that generates values
>> as needed:
>>
>> final class PlayerAudioCache {
>>
>> // MARK: Retrieving audio buffers
>>
>> func audioBufferForAssetWithName(name: String) -> AVAudioPCMBuffer? {
>> addAudioBufferForAssetWithNameIfNeeded(name)
>> return cachedAudioBuffers[name]
>> }
>>
>> // MARK: Adding audio buffers
>>
>> func addAudioBufferForAssetWithNameIfNeeded(name: String) {
>> guard cachedAudioBuffers[name] == nil else { return }
>> addAudioBufferForAssetWithName(name)
>> }
>>
>> private func addAudioBufferForAssetWithName(name: String) {
>> guard let dataAsset = NSDataAsset(name: name) else { fatalError() }
>> cachedAudioBuffers[name] = dataAsset.map { URL -> AVAudioPCMBuffer in
>> AVAudioPCMBuffer(contentsOfURL: URL)!
>> }
>> }
>>
>> private var cachedAudioBuffers: [String: AVAudioPCMBuffer] = [:]
>>
>> }
>>
>> I feel like there is a pre-made type in Swift’s standard library for what
>> I’m doing here. Am I right?
>>
>> Ideas? Pointers?
>>
>> Thank you!
>>
>> R+
>>
>> _______________________________________________
>> swift-users mailing list
>> swift-users@swift.org <mailto:swift-users@swift.org>
>> https://lists.swift.org/mailman/listinfo/swift-users
>
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