Unary operator ++ cannot be applied to an operand of type Int

Question

Why does the following swift code bring me the error "Unary operator '++' cannot be applied to an operand of type 'Int'" ??? (using swift-1.2 on Xcode-6.3.2)

struct Set {

    var player1Games: Int
    var player2Games: Int

    init() {
        self.player1Games = 0
        self.player2Games = 0
    }

    func increasePlayer1GameScore () {
        player1Games++   // error: Unary operator '++' cannot be applied to an operand of type 'Int'
    }

    func increasePlayer2GameScore () {
        player2Games++   // error: Unary operator '++' cannot be applied to an operand of type 'Int'
    }

}

Set is a inbuilt type in swift. try renaming your struct. it should work — Vivek Molkar, May 27 '15 at 08:34

Eric Aya · Answer 1 · 2015-05-28T08:28:59.110

The error message is a bit misleading. What you need to do is add mutating before func to specify that it will modify the struct:

struct MySet {

    var player1Games: Int
    var player2Games: Int

    init() {
        self.player1Games = 0
        self.player2Games = 0
    }

    mutating func increasePlayer1GameScore() {
        player1Games++
    }

    mutating func increasePlayer2GameScore() {
        player2Games++
    }

}

Note: Set is a type in Swift, I would suggest to use a different name for your struct.

score 5 · Answer 2 · answered May 27 '15 at 08:49

5

Use the mutating keyword before a function declaration to indicate you're mutating the class variables.

OR

Change your struct to a class.

This should fix your issues :).

answered May 27 '15 at 08:49

Chackle

2,249
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score 2 · Answer 3 · answered Jun 23 '18 at 17:13

2

In Swift 3 and later, the reason for this error is that the ++ and -- operators have been removed from the language. It's recommended to use x += 1 instead.

See this very good answer for more detail on why this has happened.

answered Jun 23 '18 at 17:13

Craig Brown

1,891
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1

Why was this downvoted? Anyone who finds this page through a search for that error message will probably find this is the reason for the error (it was for me). – Craig Brown Jul 17 '18 at 11:50
This was my problem, not sure why you were downvoted. – Matt Jan 04 '19 at 04:45

Unary operator ++ cannot be applied to an operand of type Int

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