Checking if an object is a given type in Swift

Question

I have an array that is made up of AnyObject  I want to iterate over it  and find all elements that are array instances   How can I check if an object is of a given type in Swift

User · Answer

If you only want to know if an object is a subtype of a given type then there is a simpler approach:

class Shape {}
class Circle : Shape {}
class Rectangle : Shape {}

func area (shape: Shape) -> Double {
  if shape is Circle { ... }
  else if shape is Rectangle { ... }
}

“Use the type check operator (is) to check whether an instance is of a certain subclass type. The type check operator returns true if the instance is of that subclass type and false if it is not.” Excerpt From: Apple Inc. “The Swift Programming Language.” iBooks.

In the above the phrase 'of a certain subclass type' is important. The use of is Circle and is Rectangle is accepted by the compiler because that value shape is declared as Shape (a superclass of Circle and Rectangle).

If you are using primitive types, the superclass would be Any. Here is an example:

 21> func test (obj:Any) -> String {
 22.     if obj is Int { return "Int" }
 23.     else if obj is String { return "String" }
 24.     else { return "Any" }
 25. } 
 ...  
 30> test (1)
$R16: String = "Int"
 31> test ("abc")
$R17: String = "String"
 32> test (nil)
$R18: String = "Any"

User · Answer

Swift 3    class Shape    class Circle   Shape    class Rectangle   Shape     if aShape isKind of  Circle self

User · Answer

Swift 4 2   In my case   using isKind function       isKind of     Returns a Boolean value that indicates whether the receiver is an instance of given class or an instance of any class that inherits from that class      let items    AnyObject      A    B            for obj in items       if obj isKind of  NSString self          print  String               Readmore https   developer apple com documentation objectivec nsobjectprotocol 1418511-iskind

User · Answer

Swift 5 2  amp  Xcode Version 11 3 1 11C504   Here is my solution of checking data type    if let typeCheck   myResult as   String   Any            print  It s Dictionary          else            print  It s not Dictionary             I hope it will help you

User · Answer

In Swift 2 2 - 5 you can now do   if object is String       Then to filter your array   let filteredArray   originalArray filter    0 is Array      If you have multiple types to check       switch object           case is String                   case is OtherClass                   default

User · Answer

If you want to check against a specific type you can do the following   if let stringArray   obj as   String           obj is a string array  Do something with stringArray   else          obj is not a string array     You can use  as   and that will throw a runtime error if obj is not of type  String   let stringArray   obj as   String    You can also check one element at a time   let items    Any      Hello    World   for obj in items      if let str   obj as  String            obj is a String  Do something with str         else            obj is not a String

User · Answer

myObject as  String returns nil if myObject is not a String  Otherwise  it returns a String   so you can access the string itself with myObject   or cast it with myObject  as String safely

User · Answer

for swift4   if obj is MyClass         then object type is MyClass Type

User · Answer

If you don t know that you will get an array of dictionaries or single dictionary in the response from server you need to check whether the result contains an array or not  In my case always receiving an array of dictionaries except once  So  to handle that I used the below code for swift 3   if let str   strDict  item   as  Array lt Any gt    Here as  Array checks whether the obtained value is array  of dictionary items   In else case you can handle if it is single dictionary item which is not kept inside an array

User · Answer

I have 2 ways of doing it   if let thisShape   aShape as  Square    Or   aShape isKindOfClass Square    Here is a detailed example    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       Edit  3 now   let myShape   Shape   if myShape is Shape       print  yes it is

User · Answer

as  won t always give you the expected result because as doesn t test if a data type is of a specific kind but only if a data type can be converted to or represented as specific kind   Consider this code for example   func handleError   error  Error         if let nsError   error as  NSError     Every data type conforming to the Error protocol can be converted to a NSError object  so this will always succeed  Yet that doesn t mean that error is in fact a NSError object or a subclass of it   A correct type check would be   func handleError   error  Error         if type of  error     NSError self     However  this checks for the exact type only  If you want to also include subclass of NSError  you should use   func handleError   error  Error         if error is NSError Type

User · Answer

Why not use the built in functionality built especially for this task   let myArray   Any      easy    as    that   let type   type of  myArray   Result   Array lt Any gt

User · Answer

Why not to use something like this  fileprivate enum types       case typeString     case typeInt     case typeDouble     case typeUnknown    fileprivate func typeOfAny variable  Any  - gt  types       if variable is String  return types typeString      if variable is Int  return types typeInt      if variable is Double  return types typeDouble      return types typeUnknown     in Swift 3

User · Answer

Assume drawTriangle is an instance of UIView To check whether drawTriangle is of type UITableView   In Swift 3   if drawTriangle is UITableView         in deed drawTriangle is UIView        do something here      else         do something here        This also could be used for classes defined by yourself  You could use this to check subviews of a view

User · Answer

If you have Response Like This        registeration method    email      is stucked   true     individual          id   24099       first name    ahmad        last name    zozoz        email   null       mobile number   null       confirmed   false       avatar    http   abc-abc-xyz amazonaws com images placeholder-profile png        doctor request status   0         max number of confirmation trials   4     max number of invalid confirmation trials   12     and you want to check for value is stucked which will be read as AnyObject  all you have to do is this  if let isStucked   response  is stucked   as  Bool    if isStucked        print  is Stucked         else        print  Not Stucked

User · Answer

Be warned about this    var string    Hello  as NSString var obj1 AnyObject   string var obj2 NSObject   string  print obj1 is NSString  print obj2 is NSString  print obj1 is String  print obj2 is String     All of the four last lines return true  this is because if you type  var r1 CGRect   CGRect   print r1 is String        it prints  false  of course  but a Warning says that the Cast from CGRect to String fails  So some type are bridged  ans the  is  keyword calls an implicit cast    You should better use one of these   myObject isKind of  MyClass self    myObject isMember of  MyClass self

User · Answer

Just for the sake of completeness based on the accepted answer and some others   let items    Any      Hello    World   1   for obj in items where obj is String         obj is a String  Do something with str     But you can also  compactMap also  maps  the values which filter doesn t    items compactMap    0 as  String   forEach     do something with  0          And a version using switch   for obj in items       switch  obj            case is Int                it s an integer         case let stringObj as String                you can do something with stringObj which is a String         default             print    type of  obj        get the type           But sticking to the question  to check if it s an array  i e   String     let items    Any      Hello    World   1    Hello    World    of    Arrays     for obj in items     if let stringArray   obj as   String        print    stringArray            Or more generally  see this other question answer    for obj in items     if obj is  Any        print  is  Any           if obj is  AnyObject        print  is  AnyObject           if obj is NSArray       print  is NSArray

User · Answer

If you just want to check the class without getting a warning because of the unused defined value  let someVariable       you can simply replace the let stuff with a boolean   if  yourObject as  ClassToCompareWith     nil         do what you have to do   else         do something else     Xcode proposed this when I used the let way and didn t use the defined value

[swift] Checking if an object is a given type in Swift

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