How to determine the type of a variable in Swift

Question

Is there a function to determine the variable type in Swift? I presume there might be something like like type() in Python.

I'd like a way to judge if a variable is a Foundation object or C variable in Swift. Like NSString vs String, or NSArray vs array. So that I can log it out in console and see clearly what it is.

For example, I would like to know the type inferred for the the first array below:

var array = [1,2,3]  // by default NSArray or array?
var array:[Int] = [1,2,3]
var array:NSArray = [1,2,3]
var array:Array<Any> = [1,2,3]

I have seen answers for judging if a given variable is a kind of given type in this question, but I'll say it's quite different from what I want to ask.

question from:https://stackoverflow.com/questions/24093433/how-to-determine-the-type-of-a-variable-in-swift

Answer 1

You can get a reference to the type object of a value by using the .dynamicType property. This is equivalent to Python's type() function, and is mentioned in the Swift documentation under Language Reference: Types: Metatype Type.

var intArray = [1, 2, 3]
let typeOfArray = intArray.dynamicType

With this type object, we are able to create a new instance of the same array type.

var newArray = typeOfArray()
newArray.append(5)
newArray.append(6)
println(newArray)

[5, 6]

We can see that this new value is of the same type ([Int]) by attempting to append a float:

newArray.append(1.5)

error: type 'Int' does not conform to protocol 'FloatLiteralConvertible'

If we import Cocoa and use an array literal with mixed types, we can see that an NSArray is created:

import Cocoa

var mixedArray = [1, "2"]
let mixedArrayType = mixedArray.dynamicType

var newArray = mixedArrayType()
var mutableArray = newArray.mutableCopy() as NSMutableArray

mutableArray.addObject(1)
mutableArray.addObject(1.5)
mutableArray.addObject("2")

println(mutableArray)

(1, "1.5", 2)

However, at this point there does not seem to be any general way to generate a string description of a type object, so this may not serve the debugging role that you were asking about.

Types derived from NSObject do have a .description() method, as is used in SiLo's answer,

println(mixedArrayType.description())

__NSArrayI

However this is not present on types such as Swift's built-in arrays.

println(typeOfArray.description())

error: '[Int].Type' does not have a member named 'description'