Swift: Binary operator '==' cannot be applied to two '() -> ()' operands

Question

Got an error when try to compare two closures:

Binary operator '==' cannot be applied to two '() -> ()' operands

How should I do this?

For example:

enum SomeEnum {
   case caseOne
   case caseTwo(closure: () -> Void)
}

let e1 = SomeEnum.caseTwo(closure: {
    print("something 1")
})
let e2 = SomeEnum.caseTwo(closure: {
    print("something 2")
})

switch (e1, e2) {
case let (.caseTwo(l), .caseTwo(r)):
    return l == r // Binary operator '==' cannot be applied to two '() -> ()' operands
    break
default: 
    break
}

Please show the source for the enum and an example of how you're using it. — Samah, Jan 31 '18 at 02:32
You can't use equality on enums with associated values. Consider rewriting your code so that you don't need to check equality at all. — Samah, Jan 31 '18 at 02:51
You can add the 2nd parameter in *caseTwo* which describes the closure, for example *UUID* or *#line* + *#file* of a place where the closure was generated — iWheelBuy, Jan 31 '18 at 02:51
@Samah yes, I was trying to use `Equatable` protocol and failed — Meniny, Jan 31 '18 at 02:53
This sounds like an XY problem. What is the main purpose of comparing `e1` and `e2`? Do you just want to find out if they are the same case? — Samah, Jan 31 '18 at 02:55
[Closures aren't equatable.](https://stackoverflow.com/a/25694072/3141234) — Alexander, Jan 31 '18 at 03:27

score 3 · Accepted Answer · answered Jan 31 '18 at 03:01

If you want to do comparisons of enums that have associated values, you will need to individually compare cases so that you can ignore the values of those that have them.

enum SomeEnum {
    case caseOne
    case caseTwo(closure: () -> Void)
    case caseThree
}

let e1 = SomeEnum.caseTwo(closure: {
    print("something 1")
})
let e2 = SomeEnum.caseTwo(closure: {
    print("something 2")
})

switch (e1, e2) {
    case (.caseOne, .caseOne), (.caseThree, .caseThree):
        print("both something else")
    case (.caseTwo, .caseTwo):
        print("both caseTwo")
    default:
        print("not equal")
}

Note that you could also join `(.caseTwo, .caseTwo)` with the others. — Samah, Jan 31 '18 at 03:03

Swift: Binary operator '==' cannot be applied to two '() -> ()' operands

1 Answers1