Swift：用于类型检查的通用函数

Question

noob question. This code has a lot of copy & paste for checking swift types. Is there a way to condense it into one generic function of some kind? Thanks for any help in advance.

import Foundation


let x: AnyObject = 42


if x is Int {
    print("x is Int")
}else {
    print("x is NOT Int")
}

if x is Double {
    print("x is Double")
}else {
    print("x is NOT Double")
}

if x is Float {
    print("x is Float")
}else {
    print("x is NOT Float")
}

if x is String {
    print("x is String")
}else {
    print("x is NOT String")
}

/* 
prints:
x is Int
x is Double
x is Float
x is NOT String
*/

Answer 1

You can call dynamicType :

print("x is \(x.dynamicType)")

In your case, since you explicit specified that x is an object ( AnyObject ) it is converted to NSNumber by the compiler. Technically, it's neither Int , nor Double , nor Float .

Answer 2

not sure what you're doing exactly, but just using is alone should work.

let x: AnyObject = 42

x is Int     // returns true
x is Double  // returns true
x is Float   // returns true
x is String  // returns false

but if you actually need a function for some other reason, then this works the exact same.

import Foundation

func checkType(value: AnyObject, type: AnyObject) -> Bool {
    if type is Int {
        if value is Int {
            return true
        } else {
            return false
        }
    } else if type is Double {
        if value is Double {
            return true
        } else {
            return false
        }
    } else if type is Float {
        if value is Float {
            return true
        } else {
            return false
        }
    } else if type is String {
        if value is String {
            return true
        } else {
            return false
        }
    }
    return false
}

let myVar: AnyObject = 42

checkType(myVar, Int())        // returns true
checkType(myVar, Double())     // returns true
checkType(myVar, Float())      // returns true
checkType(myVar, String())     // returns false

Answer 3

ok I found the solution, it's actually quite simple:

let x = 42

func checkTypeOf<Value, Type> (value: Value, type: Type) {
    if value is Type {
        print("value is \(type.dynamicType)")
    }else {
        print("value is NOT \(type.dynamicType)")
    }
}

checkTypeOf(x, type: 0)
checkTypeOf(x, type: "")

/* 
prints:
value is Int
value is NOT String
*/

the thing is the "type" parameter needs to be a placeholder value, for example 0 for Int, or an empty string if checking String, so it's not the cleanest way to do it, but Swift's type inference makes it quite usable.