Currying func in Swift 4

Question

In Swift 4, how can I curry func, or something similar:

func doSomething(a: A, b: B, c: C) {
}

let do_a = doSomething(a: value_a)
let do_ab = do_a(b: value_b)
let result = do_ab(c: value_c)

In JS, we can do:

const sum = x => y => x + y;

// returns a function y => 2 + y
sum (2);

// returns the number 3
sum (2)(1);

I read the answer in here Curry Function in Swift

But I want to ask for the current Swift (Swift 4). And can I avoid to create a generic func?

func curry<A,B,C,D,E>(f: (A, B, C, D) -> E) -> A -> B -> C -> D -> E

But it's from 2014

Thank you.

You mean currying? I think Swift once supported that but removed that feature. — Sweeper, May 23 '18 at 06:02
@rmaddy I'm sorry for the unclear question. I want something like currying. doSomething just a sudo code. — tuledev, May 23 '18 at 06:05

Sweeper · Answer 1 · 2018-05-23T07:52:12.873

3

You used to be able to do this very easily in Swift 2:

func add(a: Int)(b: Int) -> Int {
    return a + b
}

let add3 = add(3) let result = add3(b: 5) // 8

Starting from Swift 3, this is no longer valid syntax.

You'd have to do something like this:

func add(_ a: Int) -> (Int) -> Int {
    return { $0 + a }
}

For three parameters, this will be even longer and harder to understand. I recommend you not to do this.

edited May 23 '18 at 07:52

answered May 23 '18 at 06:11

Sweeper

Thank you. You are right. I know that. That why I ask this question. How to curry for every func without the long trail. I'm not sure we can achieve it in Swift 4. – tuledev May 23 '18 at 06:15
1

Swift 3 and up actually lets you write `func add(_ a: Int) -> (Int) -> Int`. – Tim Vermeulen May 23 '18 at 06:19
@TimVermeulen Do you mean I should remove the brackets? I originally added them for clarity. – Sweeper May 23 '18 at 06:20
@anhtu Look at the duplicate. It shows a `curry` function that curries a function. – Sweeper May 23 '18 at 06:22
@Sweeper thank for your help. But I think we can't do more than https://stackoverflow.com/questions/24107191/curry-function-in-swift – tuledev May 23 '18 at 06:32
@Sweeper `(A) -> (B) -> (C) -> D` is a lot more readable than `(A) -> ((B) -> ((C) -> D))` :) – Tim Vermeulen May 23 '18 at 07:48
@TimVermeulen Okay, edited. – Sweeper May 23 '18 at 07:52

1 Answers1