How does one make an optional closure in swift?

Question

I\'m trying to declare an argument in Swift that takes an optional closure. The function I have declared looks like this:

class Promise {

 func then(onFulfi         


        

Answer 1

Since I assume, that this "optional" closure should simply do nothing, you could use a parameter with an empty closure as default value:

func then(onFulfilled: ()->(), onReject: ()->() = {}){       
    // now you can call your closures
    onFulfilled()
    onReject()
}

this function can now be called with or without the onReject callback

then({ ... })
then({ ... }, onReject: { ... })

No need for Swift's awesome Optionals? here!