Created
March 5, 2018 07:45
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Declaring a lazy-initialized object with `let` in Swift
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class Lazy <T> { | |
private var t: T? | |
private let initializer: () -> T | |
private let semaphore = DispatchSemaphore(value: 1) | |
init(_ initializer: @escaping () -> T) { | |
self.initializer = initializer | |
} | |
private func initialize() -> T { | |
return self.initializer() | |
} | |
var value: T { | |
self.semaphore.wait() | |
defer { self.semaphore.signal() } | |
switch self.t { | |
case .some(let t): | |
return t | |
case .none: | |
let t = initialize() | |
defer { self.t = t } | |
return t | |
} | |
} | |
} | |
func lazy <T> (_ initializer: @escaping () -> T) -> Lazy<T> { | |
return Lazy(initializer) | |
} | |
struct A { | |
let i: Int | |
} | |
class Test { | |
let a: Lazy<A> = lazy { A(i: 1) } | |
} | |
let test = Test() | |
test.a.value.i // 1 |
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