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

问题

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'
    }

}

回答1:

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.

回答2:

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

Change your struct to a class.

This should fix your issues :).

回答3:

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.

来源：https://stackoverflow.com/questions/30477078/unary-operator-cannot-be-applied-to-an-operand-of-type-int

标签

swift

int

unary-operator