//: Playground - noun: a place where people can play

import UIKit

class A {
    class func a() {
        print("yeah")
    }

    func getInnerValue() {
        self.dynamicType.a()
    }
}

class B: A {
    override class func a() {
        print("yeah yeah")
    }
}

B.a() // yeah yeah
A.a() // yeah
B().getInnerValue() // yeah yeah
A().getInnerValue() // yeah

评论:我不明白@JérémyLapointe如何回答这个问题。使用type(of:)只能通过检查编译时信息来工作，即使实际类型是一个更特定的子类。现在在Swift 5.1中有一个更简单的方法来动态查询类型，而不需要像@Dash建议的那样诉诸dynamicType。有关我从哪里得到这些信息的更多详细信息，请参阅SE-0068:将Swift Self扩展到类成员和值类型。

Code

斯威夫特5.1

// Within an instance method context
Self.self

// Within a static method context
self

这允许使用Self作为引用包含类型(在结构、枚举和final类的情况下)或动态类型(在非final类的情况下)的简写。

解释

提案很好地解释了为什么这种方法改进了dynamicType:

Introducing Self addresses the following issues: dynamicType remains an exception to Swift's lowercased keywords rule. This change eliminates a special case that's out of step with Swift's new standards. Self is shorter and clearer in its intent. It mirrors self, which refers to the current instance. It provides an easier way to access static members. As type names grow large, readability suffers. MyExtremelyLargeTypeName.staticMember is unwieldy to type and read. Code using hardwired type names is less portable than code that automatically knows its type. Renaming a type means updating any TypeName references in code. Using self.dynamicType fights against Swift's goals of concision and clarity in that it is both noisy and esoteric. Note that self.dynamicType.classMember and TypeName.classMember may not be synonyms in class types with non-final members.

//: Playground - noun: a place where people can play

import UIKit

class A {
    class func a() {
        print("yeah")
    }

    func getInnerValue() {
        self.dynamicType.a()
    }
}

class B: A {
    override class func a() {
        print("yeah yeah")
    }
}

B.a() // yeah yeah
A.a() // yeah
B().getInnerValue() // yeah yeah
A().getInnerValue() // yeah

以下是我推荐的两种方法:

if let thisShape = aShape as? Square 

Or:

aShape.isKindOfClass(Square)

下面是一个详细的例子:

class Shape { }
class Square: Shape { } 
class Circle: Shape { }

var aShape = Shape()
aShape = Square()

if let thisShape = aShape as? Square {
    println("Its a square")
} else {
    println("Its not a square")
}

if aShape.isKindOfClass(Square) {
    println("Its a square")
} else {
    println("Its not a square")
}

如果您只是需要检查变量是否属于X类型，或者它是否符合某种协议，那么您可以使用is或as?具体如下:

var unknownTypeVariable = …

if unknownTypeVariable is <ClassName> {
    //the variable is of type <ClassName>
} else {
    //variable is not of type <ClassName>
}

这相当于Obj-C中的isKindOfClass。

这等价于conformsToProtocol或isMemberOfClass

var unknownTypeVariable = …

if let myClass = unknownTypeVariable as? <ClassName or ProtocolName> {
    //unknownTypeVarible is of type <ClassName or ProtocolName>
} else {
    //unknownTypeVariable is not of type <ClassName or ProtocolName>
}

这取决于用例。但是让我们假设您想要对“变量”类型做一些有用的事情。Swift switch语句非常强大，可以帮助你得到你想要的结果…

    let dd2 = ["x" : 9, "y" : "home9"]
    let dds = dd2.filter {
        let eIndex = "x"
        let eValue:Any = 9
        var r = false

        switch eValue {
        case let testString as String:
            r = $1 == testString
        case let testUInt as UInt:
            r = $1 == testUInt
        case let testInt as Int:
            r = $1 == testInt
        default:
            r = false
        }

        return r && $0 == eIndex
    }

在这种情况下，有一个简单的字典，其中包含键/值对，可以是UInt, Int或String。在字典上的.filter()方法中，我需要确保正确地测试值，并且只在字符串时测试字符串，等等。switch语句使此操作简单而安全! 通过将9赋值给Any类型的变量，它将执行Int类型的转换。试着把它改成:

   let eValue:Any = "home9"

．．再试一次。这一次，它执行了as String的情况。