swift - 二元运算符 '==' 不能应用于 if 语句中的两个操作数

Question

给定以下结构:

struct Landmark {
    let id: String
    let name: String
    let location: CLLocationCoordinate2D
}

以及以下@State:

@State var landmarks: [Landmark] = [
    Landmark(id: "1", name: "Sydney Harbour Bridge", location: .init(latitude: -33.852222, longitude: 151.210556)),
    Landmark(id: "2", name: "Brooklyn Bridge", location: .init(latitude: 40.706, longitude: -73.997))
]

private func selectNextLandmark() {
    if let selectedLandmark = selectedLandmark, let currentIndex = landmarks.firstIndex(where: { $0 == selectedLandmark }), currentIndex + 1 < landmarks.endIndex {
        self.selectedLandmark = landmarks[currentIndex + 1]
    } else {
        selectedLandmark = landmarks.first
    }
}

我在 selectNextLandmark 内的 if 行收到以下错误:

Operator function '==' requires that 'Landmark' conform to 'Equatable'

我的 Landmark struct 是否有问题，或者 if 语句语法有问题吗？

Answer 1

信息很明确

Operator function '==' requires that 'Landmark' conform to 'Equatable'

结构体Landmark必须符合Equatable协议(protocol)，以便它知道相对于结构体的相等性意味着什么。将您的结构更新为

struct Landmark: Equatable {
    let id: String
    let name: String
    let location: CLLocationCoordinate2D

    static func == (lhs: Landmark, rhs: Landmark) -> Bool {
        //Your equating logic here
    }
}