Created
November 14, 2014 18:52
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Memoization in Swift
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| class Memo<T> { | |
| private let closure: () -> T; | |
| private var result: T? | |
| var value: T { | |
| if let value = result { | |
| return value | |
| } else { | |
| let value = closure() | |
| println("computed \(value)") | |
| result = value | |
| return value | |
| } | |
| } | |
| init(_ closure: () -> T) { | |
| self.closure = closure | |
| } | |
| deinit { | |
| println("memo destroyed") | |
| } | |
| func invalidate() { | |
| result = nil | |
| } | |
| } | |
| private func factorial(n: Int) -> Int { | |
| if n <= 0 { | |
| return 1 | |
| } else { | |
| return n * factorial(n - 1) | |
| } | |
| } | |
| class Sample { | |
| lazy var memo: Memo<Int> = Memo { [unowned self] in factorial(self.degree) } | |
| var degree: Int = 3 { | |
| didSet { | |
| if degree != oldValue { | |
| memo.invalidate() | |
| } | |
| } | |
| } | |
| init() {} | |
| deinit { | |
| println("memo owner destroyed") | |
| } | |
| } | |
| var sample: Sample! = Sample() | |
| println(sample.memo.value) | |
| println(sample.memo.value) | |
| println(sample.memo.value) | |
| sample.degree = 20 | |
| println(sample.memo.value) | |
| println(sample.memo.value) | |
| println(sample.memo.value) | |
| sample.degree = 5 | |
| println(sample.memo.value) | |
| println(sample.memo.value) | |
| println(sample.memo.value) | |
| sample = nil |
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