tasks a-s

Task/Polymorphic-copy/Objective-C/polymorphic-copy.m

@@ -0,0 +1,39 @@
+@interface T : NSObject
+{ }
+- (void)identify;
+@end
+
+@implementation T
+- (void)identify {
+    NSLog(@"I am a genuine T");
+}
+- (id)copyWithZone:(NSZone *)zone {
+    T *copy = [[[self class] allocWithZone:zone] init]; // call an appropriate constructor here
+                                                        // then copy data into it as appropriate here
+                                                        // make sure to use "[[self class] alloc..." and
+                                                        // not "[T alloc..." to make it polymorphic
+    return copy;
+}
+@end
+
+@interface S : T
+{ }
+@end
+
+@implementation S
+- (void)identify
+{
+    NSLog(@"I am an S");
+}
+@end
+
+int main()
+{
+    T *original = [[S alloc] init];
+    T *another = [original copy];
+    [another identify]; // logs "I am an S"
+
+    [another release]; // like "alloc", the object returned by "copy" is "owned" by the caller, so we are responsible for releasing it
+    [original release];
+    return 0;
+}