Example of dispatch_once in Swift

Question

Is there an example of how dispatch_once should be used in Swift? (Preferably one from Apple.)

Note: In this case, I\'m not using it for a singleton

Answer 1

the robertvojta's answer is probably the best. because i try always to avoid import Foundation and use 'pure' Swift solution (with Swift3.0 i could change my opinion), I would like to share with you my own, very simple approach. i hope, this code is self-explanatory

class C {
    private var i: Int?
    func foo()->Void {
        defer {
            i = 0
        }
        guard i == nil else { return }
        print("runs once")
    }
}

let c = C()
c.foo() // prints "runs once"
c.foo()
c.foo()

let c1 = C()
c1.foo() // prints "runs once"
c1.foo()

class D {
    static private var i: Int?
    func foo()->Void {
        defer {
            D.i = 0
        }
        guard D.i == nil else { return }
        print("runs once")
    }
}

let d = D()
d.foo() // prints "runs once"
d.foo()
let d2 = D()
d.foo()