A Swift class to dispatch blocks either the first time and or all but the first time.

FirstTimeOrAnother.swift

import Foundation

public final class FirstOrAllOtherDispatcher {
    
    private var firstTimeOnlyBlock: (()->Void)?
    private var allOtherTimesBlock: (()->Void)?
    
    public init(firstTime: ()->Void) {
        self.firstTimeOnlyBlock = firstTime
        self.allOtherTimesBlock = nil
    }
    
    public init(allButFirstBlock: ()->Void) {
        self.firstTimeOnlyBlock = nil
        self.allOtherTimesBlock = allButFirstBlock
    }
    
    public init(firstTime: ()->Void, allOtherTimes: ()->Void) {
        self.firstTimeOnlyBlock = firstTime
        self.allOtherTimesBlock = allOtherTimes
    }
    
    
    private var once: dispatch_once_t = 0
    private func makeSwizzle() {
        dispatch_once(&once, {
            let myclass: AnyClass = object_getClass(self)
            let originalMethod = class_getInstanceMethod(myclass, "doing")
            let swizzledMethod = class_getInstanceMethod(myclass, "realDoing")
            method_exchangeImplementations(originalMethod, swizzledMethod)
        })
    }
    
    /// This has to be dynamic, can be private
    private dynamic func doing() {
        makeSwizzle()
        firstTimeOnlyBlock?()
    }
    
    /// Has to be at least internal or be private dynamic
    private dynamic func realDoing() {
        allOtherTimesBlock?()
    }
    
    
    public func call() {
        doing()
    }
    
}


let tt = FirstOrAllOtherDispatcher(firstTime: { print("Fisrt and once") }, allOtherTimes: { print("Other time") })
tt.call()
tt.call()