The more I think about this, the more obvious it sounds. And the more I think about it, the less I believe it deserves a post. But it was a pleasant surprise anyway, so here it goes.
Let’s assume we have an Objective-C project, that contains a class like this:
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//Person.h @interface Person : NSObject @property (nonatomic, copy, readonly) NSString *name; @property (nonatomic, assign, readonly) NSInteger age; - (instancetype) initWithName: (NSString *) name age: (NSInteger) age; @end //Person.m #import "Person.h" @interface Person() @property (nonatomic, copy, readwrite) NSString *name; @property (nonatomic, assign, readwrite) NSInteger age; @end @implementation Person - (instancetype) initWithName: (NSString *) name age: (NSInteger) age { if (self = [super init]) { _name = name; _age = age; } return self; } @end |
And it also contains another class like this:
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//Movie.h @interface Movie : NSObject @property (nonatomic, copy, readonly) NSString *title; @property (nonatomic, copy, readonly) NSString *director; - (instancetype) initWithTitle: (NSString *) title director: (NSString *) director; @end //Movie.m #import "Movie.h" @interface Movie() @property (nonatomic, copy, readwrite) NSString *title; @property (nonatomic, copy, readwrite) NSString *director; @end @implementation Movie - (instancetype) initWithTitle: (NSString *) title director: (NSString *) director { if (self = [super init]) { _title = title; _director = director; } return self; } @end |
Now, let’s say we declare a Swift protocol like this:
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@objc protocol Displayable { var firstLineContent: String { get } var secondLineContent: String { get } } |
And extensions to the Person and Movie object to enforce compliance with the Displayable protocol:
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extension Person: Displayable { var firstLineContent: String { return "Name \(name)" } var secondLineContent: String { return "Age \(age)" } } extension Movie: Displayable { var firstLineContent: String { return "Title \(title)" } var secondLineContent: String { return "Director \(director)" } } |
Now, we can consume the Displayable protocol from Swift:
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final class TableBuilder: NSObject { override init() { super.init() printAllTheThings() } private func printAllTheThings() { let items = getItems() for displayable in items { print("Swift: First line: ", displayable.firstLineContent) print("Swift: Second line: ", displayable.secondLineContent) } } private func getItems( ) -> [Displayable] { let meFakingMyAge = Person(name: "Cesar", age: 21) let movie = Movie(title: "The Quiet Man", director: "John Ford") return [meFakingMyAge, movie] } } |
Or from Objective-C (please, excuse the weakness of my ObjC-generics kung fu):
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#import "TableBuilderObjC.h" #import "ProtocolExtensionsInterop-Swift.h" @implementation TableBuilderObjC - (instancetype) init { if (self = [super init]) { [self printAllTheThings]; } return self; } - (void) printAllTheThings { NSLog(@"printing from Obj-C ========"); NSArray<NSObject<Displayable> *> *items = [self buildItems]; for (NSObject<Displayable> *item in items) { NSLog(@"ObjC: first Line %@", [item firstLineContent]); NSLog(@"ObjC: second line %@", [item secondLineContent]); } } - (NSArray<NSObject<Displayable> *> *) buildItems { Person *meFakingMyAge = [[Person alloc] initWithName: @"Cesar" age: 21]; Movie *theQuiteMan = [[Movie alloc] initWithTitle: @"The Quiet Man" director: @"John Ford"]; NSMutableArray<NSObject<Displayable> *> *returnValue = [[NSMutableArray alloc] initWithCapacity:2]; [returnValue addObject:meFakingMyAge]; [returnValue addObject:theQuiteMan]; return returnValue; } @end |
Which, believe me, is a huge relief when dealing with large legacy projects.
In case you want to play with a complete example, I uploaded a sample project to GitHub.
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