Merge pull request #26 from rakaramos/source

wojteklu · wojteklu · commit ec1e76a64e36 · 2015-10-07T20:42:04.000+02:00
Add "Easy cast with _ObjectiveCBridgeable" hint
diff --git a/source/_posts/2015-10-07-easy-cast-with-_ObjectiveCBridgeable.markdown b/source/_posts/2015-10-07-easy-cast-with-_ObjectiveCBridgeable.markdown
@@ -0,0 +1,88 @@
+---
+layout: post
+title: "Easy cast with _ObjectiveCBridgeable"
+date: 2015-10-07 19:15:43 +0200
+comments: true
+author: rafa
+categories:
+---
+
+Swift is out there for about a year and it's a great programming language. I think that almost every iOS/OSX developer out there has already written couple of things in Swift (if you haven't, go ahead and try, you won't regret it, I promise). Although, we have many years of libs and frameworks built using Objective-C and sooner or later a project may have both Swift and Objective-C working together.
+
+Fortunately, Apple gave us a [book](https://itunes.apple.com/us/book/using-swift-cocoa-objective/id888894773?mt=11) and a couple of WWDC session ([here](https://developer.apple.com/videos/play/wwdc2014-406/) and [here](https://developer.apple.com/videos/play/wwdc2015-401/)) with the intent to help developers on this task.
+
+For those who have some experience with this integration knows that casting plays an important role. So, todays hint will dig into an poor documented protocol called `_ObjectiveCBridgeable`.
+
+The documentation, which is only founded in header files says:
+
+> A Swift Array or Dictionary of types conforming to _ObjectiveCBridgeable can be passed to Objective-C as an NSArray or NSDictionary, respectively. The elements of the resulting NSArray or NSDictionary will be the result of calling _bridgeToObjectiveC on each element of the source container.
+
+Ok, but there is something else you can do with that, which is very handy.
+
+Suppose that you have this class in Objective-C:
+
+```objc
+@interface OPerson: NSObject
+
+- (instancetype)initWithName:(NSString *)name surname:(NSString *)surname;
+
+@property (nonatomic, copy) (NSString *)name;
+@property (nonatomic, copy) (NSString *)surname;
+
+@end
+```
+
+Now you want to easily cast this class into a Swift struct. Yes, we can! All you have to do is conform to `_ObjectiveCBridgeable`, like so:
+
+```swift
+struct Person {
+        let name: String
+        let surname: String
+}
+
+extension Person: _ObjectiveCBridgeable {
+
+    typealias _ObjectiveCType = OPerson
+
+    static func _isBridgedToObjectiveC() -> Bool {
+            return type
+    }
+
+    static func _getObjectiveCType() -> Any.Type {
+            return ObjectiveCType.self
+    }
+
+    func _bridgeToObjectiveC() -> _ObjectiveCType {
+            return OPerson(name: name, surname: surname)
+    }
+
+    static func _forceBridgeFromObjectiveC(source: _ObjectiveCType, inout result: Person?) {
+            result = Person(name: source.name, surname: source.name)
+    }
+
+    static func _conditionallyBridgeFRomObjectiveC(source: _ObjectiveCType, inout result: Person?) -> Bool {
+            _forceBridgeFromObjectiveC(source, result: &result)
+            return true
+    }
+}
+```
+
+And voilá!
+
+```swift
+
+let objcPerson = OPerson(name: "John", surname: "Doe")
+
+if let swiftPerson = objcPerson as? Person {
+	//will work
+}
+
+let swiftPerson = objcPerson as Person //this too!
+
+let swiftPerson2 = Person(name: "Jack", surname:"Doe")
+let objcPerson = swiftPerson2 as OPerson //and that
+
+let person: OPerson = Person(name: "Alfred", surname: "Doe") //hooray
+```
+
+Oh, that's so beautiful, don't you think? :]
