How swift2 and swift3 datatypes mapped with Objective-C APIs

Swift 3 interfaces with Objective-C APIs in a more powerful way than previous versions. For instance,

Swift 2 mapped the id type in Objective-C to the AnyObject type in Swift, which normally can hold only values of class types. Swift 2 also provided implicit conversions to AnyObject for some bridged value types, such as String, Array, Dictionary, Set, and some numbers, as a convenience so that the native Swift types could be used easily with Cocoa APIs that expected NSString, NSArray, or the other container classes from Foundation. These conversions were inconsistent with the rest of the language, making it difficult to understand what exactly could be used as an AnyObject, resulting in bugs.

In Swift 3, the id type in Objective-C now maps to the Any type in Swift, which describes a value of any type, whether a class, enum, struct, or any other Swift type. This change makes Objective-C APIs more flexible in Swift, because Swift-defined value types can be passed to Objective-C APIs and extracted as Swift types, eliminating the need for manual “box” types. These benefits also extend to collections: Objective-C collection types NSArray, NSDictionary, and NSSet, which previously only accepted elements of AnyObject, now can hold elements of Any type. For hashed containers, such as Dictionary and Set, there’s a new type AnyHashable that can hold a value of any type conforming to the Swift Hashable protocol.

In summary, the following type mappings change from Swift 2 to Swift 3: