Swift: Test class type in switch statement

问题:

In Swift you can check the class type of an object using 'is'. How can I incorporate this into a 'switch' block?

I think it's not possible, so I'm wondering what is the best way around this.

TIA, Peter.

回答1:

You absolutely can use is in a switch block. See "Type Casting for Any and AnyObject" in the Swift Programming Language (though it's not limited to Any of course). They have an extensive example:

for thing in things {
    switch thing {
    case 0 as Int:
        println("zero as an Int")
    case 0 as Double:
        println("zero as a Double")
    case let someInt as Int:
        println("an integer value of \(someInt)")
    case let someDouble as Double where someDouble > 0:
        println("a positive double value of \(someDouble)")
// here it comes:
    case is Double:
        println("some other double value that I don't want to print")
    case let someString as String:
        println("a string value of \"\(someString)\"")
    case let (x, y) as (Double, Double):
        println("an (x, y) point at \(x), \(y)")
    case let movie as Movie:
        println("a movie called '\(movie.name)', dir. \(movie.director)")
    default:
        println("something else")
    }
}

回答2:

Putting up the example for "case is - case is Int, is String:" operation, where multiple cases can be used clubbed together to perform the same activity for Similar Object types. Here "," separating the types in case is operating like a OR operator.

switch value{
case is Int, is String:
    if value is Int{
        print("Integer::\(value)")
    }else{
        print("String::\(value)")
    }
default:
    print("\(value)")
}

Demo Link

回答3:

In case you don't have a value, just any class:

func testIsString(aClass: AnyClass) {  
  switch aClass {  
  case is NSString.Type:  
    print(true)  
  default:  
    print(false)  
  }  
}  

testIsString(NSString.self) //->true  

let value: NSString = "some string value" 
testIsString(value.dynamicType) //->true  

回答4:

I like this syntax:

switch thing {
case _ as Int: print("thing is Int")
case _ as Double: print("thing is Double")
}

since it gives you the possibility to extend the functionality fast, like this:

switch thing {
case let myInt as Int: print("\(myInt) is Int")
case _ as Double: print("thing is Double")
}