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Swift 4中,许多基金会团队已经讨论过与Swift 3相比,使用keyPaths要容易得多.这引出了一个问题……什么是keyPath？说真的,我找不到任何明确的资源.
Objective-C能够动态而不是直接引用属性.这些引用称为keypaths.它们与直接属性访问不同,因为它们实际上不读取或写入值,它们只是将其存放以供使用.
原文链接：https://www.f2er.com/swift/319513.html让我们定义一个名为Cavaliers的结构和一个名为Player的结构,然后创建每个结构的一个实例：
// an example struct
struct Player {
var name: String
var rank: String
}
// another example struct,this time with a method
struct Cavaliers {
var name: String
var maxPoint: Double
var captain: Player
func goTomaxPoint() {
print("\(name) is now travelling at warp \(maxPoint)")
}
}
// create instances of those two structs
let james = Player(name: "Lebron",rank: "Captain")
let irving = Cavaliers(name: "Kyrie",maxPoint: 9.975,captain: james)
// grab a reference to the `goTomaxPoint()` method
let score = irving.goTomaxPoint
// call that reference
score()
最后一行创建了一个名为score的goTomaxPoint()方法的引用.问题是,我们不能创建对队长名称属性的引用,但keypath可以做.
let nameKeyPath = \Cavaliers.name let maxPointKeyPath = \Cavaliers.maxPoint let captainName = \Cavaliers.captain.name let cavaliersName = irving[keyPath: nameKeyPath] let cavaliersMaxPoint = irving[keyPath: maxPointKeyPath] let cavaliersNameCaptain = irving[keyPath: captainName]
请使用Xcode 9或功能快照进行测试.
