Fun interfaces.md

Fun interfaces

You can't create an anonymous class in Swift.

Explanations

In Kotlin, using fun interface-s you can use a more convenient syntax to describe the creation of anonymous lambdas:

fun interface FunInterfaceExample {
    fun singleFunctionInInterface(funInterfaceExample: String): String
}

interface NotFunInterface {
    fun singleFunctionInInterface(funInterfaceExample: String): String
}

fun example() {
    val notFun = object : NotFunInterface {
        override fun singleFunctionInInterface(funInterfaceExample: String): String {
            return "return"
        }
    }

    val listener = FunInterfaceExample {
        println("it: ${it}")
        "some return value"
    }
}

Swift does not have a similar syntax for describing anonymous classes. You can, of course, do it as in one of the answers on StackOverflow, but it seems like some kind of big overhead:

class EmptyClass {

    var someFunc: () -> () = { }

    init(overrides: (EmptyClass) -> EmptyClass) {
        overrides(self)
    }
}

// Now you initialize 'EmptyClass' with a closure that sets
// whatever variable properties you want to override:

let workingClass = EmptyClass { ec in
    ec.someFunc = { print("It worked!") }
    return ec
}

workingClass.someFunc()  // Outputs: "It worked!"

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