You can write a Swift extension and use it in Objective-C code. Tested with Xcode 6.1.1. All you need to do is: create your extension in Swift (@objc annotation needed since Swift 4.0.3) #import “ProjectTarget-Swift.h” in your Objective-C class (where “ProjectTarget” represents the XCode target the Swift extension is associated with) call the methods from … Read more
Extensions cannot contain stored instance properties. Why? Because adding an instance property would change the size of instances of that type. What happens if one module adds an extension such that an Int is now 2 words long? What should then happen when it, for example, gets an Int from another module where they are … Read more
It seems that overriding methods and properties in an extension works with the current Swift (Swift 1.1/Xcode 6.1) only for Objective-C compatible methods and properties. If a class is derived from NSObject then all its members are automatically available in Objective-C (if possible, see below). So with class A : NSObject { } your example … Read more
1. Using default implementations (preferred). protocol MyProtocol { func doSomething() } extension MyProtocol { func doSomething() { /* return a default value or just leave empty */ } } struct MyStruct: MyProtocol { /* no compile error */ } Advantages No Objective-C runtime is involved (well, no explicitly at least). This means you can conform … Read more
As of Swift 2.0, you don’t need to write your own extension to filter nil values from an Array, you can use flatMap, which flattens the Array and filters nils: let optionals : [String?] = [“a”, “b”, nil, “d”] let nonOptionals = optionals.flatMap{$0} print(nonOptionals) Prints: [a, b, d] Note: There are 2 flatMap functions: One … Read more
If you want to extend only array with specific type. You should extend _ArrayType protocol. extension _ArrayType where Generator.Element == Int { func doSomething() { … } } If you extend Array you can only make sure your element is conformed some protocol else. i.e: extension Array where Element: Equatable { func doSomething() { … … Read more
1. Using default implementations (preferred). protocol MyProtocol { func doSomething() } extension MyProtocol { func doSomething() { /* return a default value or just leave empty */ } } struct MyStruct: MyProtocol { /* no compile error */ } Advantages No Objective-C runtime is involved (well, no explicitly at least). This means you can conform … Read more
I see no reason why the compiler shouldn’t be able to resolve this function call, therefore I would consider it a bug (it has already been filed – see SR-2450). It seems to occur whenever attempting to call a top-level function with the same name, but unambiguously different signature to a method or property that’s … Read more
Similar as in Using ‘self’ in class extension functions in Swift, you can define a generic helper method which infers the type of self from the calling context: extension UIViewController { class func instantiateFromStoryboard(storyboardName: String, storyboardId: String) -> Self { return instantiateFromStoryboardHelper(storyboardName, storyboardId: storyboardId) } private class func instantiateFromStoryboardHelper<T>(storyboardName: String, storyboardId: String) -> T { … Read more
Extensions cannot/should not override. It is not possible to override functionality (like properties or methods) in extensions as documented in Apple’s Swift Guide. Extensions can add new functionality to a type, but they cannot override existing functionality. Swift Developer Guide The compiler is allowing you to override in the extension for compatibility with Objective-C. But … Read more