Objective-C 中方法的重載，覆蓋和隱藏

在C++中，類方法有重載（overload）、覆蓋（override）和隱藏（hide）的概念（當然，函數也可重載。）。

C++的覆蓋和隱藏是個非常容易混淆的概念，尤其隱藏。學到Objective-C，因為它與C++有相似的地方，所以對此也格外留心。

從下面代碼測試結果可以看出，OC遠沒有C++那麼“靈活”。具體結論輸出資訊一目瞭然。

/**<br /> * test_Hide.m<br /> */ </p><p>#import <Foundation/Foundation.h> </p><p>// ---- @interface section ---- </p><p>// Base<br />@interface Base: NSObject<br />/* {} */ // It's optional.<br />+ (void) foo;<br />+ (void) foo: (int)param;<br />+ (void) foo: (int)param and: (int)param2;<br />+ (void) foo: (int)param and: (int)param2 and: (int)param3;<br />- (void) bar;<br />- (void) bar: (int)param;<br />- (void) bar: (int)param and: (int)param2;<br />- (void) bar: (int)param and: (int)param2 and: (int)param3;<br />@end </p><p>// Derived<br />@interface Derived: Base<br />+ (void) foo: (int)param;<br />- (void) bar: (int)param and: (int)param2;<br />@end </p><p>// ---- program section ---- </p><p>int main(int argc, char* argv[])<br />{<br /> NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init]; </p><p> [Base foo];<br /> [Base foo: 1];<br /> [Base foo: 1 and: 2];<br /> [Base foo: 1 and: 2 and: 3]; </p><p> Base* base = [[Base alloc] init];<br /> [base bar];<br /> [base bar: 1];<br /> [base bar: 1 and: 2];<br /> [base bar: 1 and: 2 and: 3];<br /> [base release]; </p><p> NSLog(@"--------< 1 >--------"); </p><p> [Derived foo]; // Ok, either! NOT hided.<br /> [Derived foo: 11]; // OK<br /> [Derived foo: 11 and: 22]; // Ok, either! NOT hided.<br /> [Derived foo: 11 and: 22 and: 33]; // Ok, either! NOT hided. </p><p> Derived* derived = [[Derived alloc] init];<br /> [derived bar]; // Ok, either! NOT hided.<br /> [derived bar: 11]; // Ok, either! NOT hided.<br /> [derived bar: 11 and: 22]; // OK<br /> [derived bar: 11 and: 22 and: 33]; // Ok, either! NOT hided.<br /> [derived release]; </p><p> NSLog(@"--------< 2 >--------"); </p><p> [pool drain];<br /> return 0;<br />}</p><p>// ---- @implementation section ---- </p><p>// Base<br />@implementation Base/* : NSObject */ // It's optional.<br />+ (void) foo<br />{<br /> NSLog(@"Base::foo");<br />}</p><p>+ (void) foo: (int)param<br />{<br /> NSLog(@"Base::foo: %i", param);<br />}</p><p>+ (void) foo: (int)param and: (int)param2<br />{<br /> NSLog(@"Base::foo: %i and: %i", param, param2);<br />}</p><p>+ (void) foo: (int)param and: (int)param2 and: (int)param3<br />{<br /> NSLog(@"Base::foo: %i and: %i and: %i", param, param2, param3);<br />}</p><p>- (void) bar<br />{<br /> NSLog(@"Base::bar");<br />}</p><p>- (void) bar: (int)param<br />{<br /> NSLog(@"Base::bar: %i", param);<br />}</p><p>- (void) bar: (int)param and: (int)param2<br />{<br /> NSLog(@"Base::bar: %i and: %i", param, param2);<br />}</p><p>- (void) bar: (int)param and: (int)param2 and: (int)param3<br />{<br /> NSLog(@"Base::bar: %i and: %i and: %i", param, param2, param3);<br />}<br />@end </p><p>// Derived<br />@implementation Derived<br />+ (void) foo: (int)param<br />{<br /> NSLog(@"Derived::foo: %i", param);<br />}</p><p>- (void) bar: (int)param and: (int)param2<br />{<br /> NSLog(@"Derived::bar: %i and: %i", param, param2);<br />}<br />@end<br />

// Output </p><p>2010-12-24 03:31:20.642 test_Hide[3700] Base::foo<br />2010-12-24 03:31:20.658 test_Hide[3700] Base::foo: 1<br />2010-12-24 03:31:20.658 test_Hide[3700] Base::foo: 1 and: 2<br />2010-12-24 03:31:20.658 test_Hide[3700] Base::foo: 1 and: 2 and: 3<br />2010-12-24 03:31:20.673 test_Hide[3700] Base::bar<br />2010-12-24 03:31:20.673 test_Hide[3700] Base::bar: 1<br />2010-12-24 03:31:20.673 test_Hide[3700] Base::bar: 1 and: 2<br />2010-12-24 03:31:20.689 test_Hide[3700] Base::bar: 1 and: 2 and: 3<br />2010-12-24 03:31:20.689 test_Hide[3700] --------< 1 >--------<br />2010-12-24 03:31:20.689 test_Hide[3700] Base::foo<br />2010-12-24 03:31:20.705 test_Hide[3700] Derived::foo: 11<br />2010-12-24 03:31:20.705 test_Hide[3700] Base::foo: 11 and: 22<br />2010-12-24 03:31:20.705 test_Hide[3700] Base::foo: 11 and: 22 and: 33<br />2010-12-24 03:31:20.720 test_Hide[3700] Base::bar<br />2010-12-24 03:31:20.720 test_Hide[3700] Base::bar: 11<br />2010-12-24 03:31:20.720 test_Hide[3700] Derived::bar: 11 and: 22<br />2010-12-24 03:31:20.736 test_Hide[3700] Base::bar: 11 and: 22 and: 33<br />2010-12-24 03:31:20.736 test_Hide[3700] --------< 2 >--------