I wonder why operator overriding is like this.

Question

Created Jul ’22

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I wonder how the + function is used directly.

extension CGPoint {

    static func add(lhs: Self, rhs: Self) -> CGPoint {

        CGPoint(x: lhs.x + rhs.x, y: lhs.y + rhs.y)

    }

    static func +(lhs: Self, rhs: Self) -> CGPoint {

        CGPoint(x: lhs.x + rhs.x, y: lhs.y + rhs.y)

    }

}



private func testCGPoint() {

    let dummy1 = CGPoint(x: 2, y: 3)

    let dummy2 = CGPoint(x: 4, y: 5)

    let dummy3: CGPoint = .add(lhs: dummy1, rhs: dummy2)

    let dummy4: CGPoint = dummy1 + dummy2

}

in my expectation, I thought that the + function would be used like the add function. i thought this form.

CGPoint.+(lhs: dummy1, rhs: dummy2)

But the + function did not.

How are you doing this?

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Answer 1

mikeyh OP

Jul ’22

Accepted Answer

A Swift expert may provide a better answer.

+ is the builtin standard infix operator equivalent to infix operator +: AdditionPrecedence which you are overriding by extending CGPoint (vs add which is just a plain old static function and cannot be used as an infix operator between two targets).

https://developer.apple.com/documentation/swift/operator-declarations

You can define your own custom infix operator (with naming restricted to specific characters) like this: (although recommend against this)

infix operator ✜: AdditionPrecedence // heavy open centre cross

extension CGPoint {

    static func ✜(lhs: Self, rhs: Self) -> CGPoint {

        CGPoint(x: lhs.x + rhs.x, y: lhs.y + rhs.y)
    }
}

private func testCGPoint() {

    print(CGPoint(x: 2, y: 3) ✜ CGPoint(x: 4, y: 5))
}

https://docs.swift.org/swift-book/LanguageGuide/AdvancedOperators.html#ID46 (Custom Operators)

https://docs.swift.org/swift-book/ReferenceManual/LexicalStructure.html#ID418 (Lexical Structure - Operators)

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