update

Task/Delegates/Objective-C/delegates-2.m

@@ -0,0 +1,45 @@
+#import <Foundation/Foundation.h>
+
+// Formal protocol for the delegate
+@protocol DelegatorDelegatingProtocol
+    - (NSString *)thing;
+@end
+
+@interface Delegator : NSObject
+    @property (weak) id delegate;
+    - (NSString *)operation;
+@end
+@implementation Delegator
+    - (NSString *)operation {
+        if ([self.delegate respondsToSelector: @selector(thing)])
+            return [self.delegate thing];
+
+        return @"default implementation";
+    }
+@end
+
+@interface Delegate : NSObject
+    <DelegatorDelegatingProtocol>
+@end
+@implementation Delegate
+    - (NSString *)thing { return @"delegate implementation"; }
+@end
+
+// Example usage with Automatic Reference Counting
+int main() {
+    @autoreleasepool {
+        // Without a delegate:
+        Delegator *a = [Delegator new];
+        NSLog(@"%@", [a operation]);    // prints "default implementation"
+
+        // With a delegate that does not implement thing:
+        a.delegate = @"A delegate may be any object";
+        NSLog(@"%@", [a operation]);    // prints "default implementation"
+
+        // With a delegate that implements "thing":
+        Delegate *d = [Delegate new];
+        a.delegate = d;
+        NSLog(@"%@", [a operation]);    // prints "delegate implementation"
+    }
+    return 0;
+}