How can I define a postfix operator on a tuple?

Question

I have the following code:

postfix operator ^^^
public postfix func ^^^(lhs: Int) -> Int {
    return 0
}

public postfix func ^^^<T>(lhs: (T, T)) -> [T] {
    return [lhs.0, lhs.1]
}

func go() {
    1^^^ // this works
    (0, 0)^^^ // error: Unary operator '^^^' cannot be applied to an operand of type '(Int, Int)'
}

For which I get the error, Unary operator '^^^' cannot be applied to an operand of type '(Int, Int)'. Any ideas how to fix this?

Yes, I see what you mean! Looks like postfix operators don't work with tuples. Not very surprising really. Maybe you could use a struct instead in your real use case. Tuples are really a sort of substandard type and there are a lot of things they don't do (for example, tuple equality has always been a major issue as well). — matt, Mar 22 '19 at 18:05
Never even thought about define operators on tuples. Though if I saw `(0, 0)^^^` in a codebase, heads would roll :p — Alexander, Mar 22 '19 at 18:06
Tuples have some very nice uses as sequences, e.g.: `(x, y, width, height) = ("x", "y", "width", "height")^^^.map { dict[$0] }` would get a frame from a dictionary of `String` to `Int`. — meisel, Mar 22 '19 at 18:06
@Alexander I just used `^^^` to make it *very* clear this was not an existing operator with conflicts :P — meisel, Mar 22 '19 at 18:07
The big reason operators are nice for tuples is because you can't extend them, so adding methods is out of the question. *And* you can do infix operators on tuples. Just not postfix I guess? — meisel, Mar 22 '19 at 18:08

score 3 · Accepted Answer · answered Mar 22 '19 at 18:14

That is a known bug, compare Prefix and postfix operators not working for tuple types in the Swift forum and SR-294 Strange errors for unary prefix operator with tuple arg.

It has been fixed for Swift 5, the following compiles and runs in Xcode 10.2 beta 4:

postfix operator ^^^

public postfix func ^^^<T>(lhs: (T, T)) -> [T] {
    return [lhs.0, lhs.1]
}

let x = (0, 0)^^^
print(x) // [0, 0]

How can I define a postfix operator on a tuple?

1 Answers1