Re: extending c++ classes and enumerations

"" <>
6 Dec 2006 12:10:19 -0500
alex skrev:

Not sure about extending classes, but enums... Let's add:

extend enum ThreadState { ANOTHER_STATE };

extend enum ThreadState { YET_ANOTHER_STATE };

And then the real value of ANOTHER_STATE will depend on the order of
header inclusions :)

No, not really. :-) If enums are defined in polymorphical classes, the
order can be preserved.

// Thread.h
class Thread {
 enum ThreadState { ERROR = -1, RUNNING, TERMINATED };

// CancelableThread.h
class CancelableThread : public Thread {
 extend enum ThreadState { CANCELLED };

// Enum2.h
class MyThread1 : public CancelableThread {
 extend enum ThreadState { ANOTHER_STATE };

// Enum3.h
class MyThread2 : public MyThread1 {
  extend enum ThreadState { YET_ANOTHER_STATE };

I should be honesty and confess my primary thoughts is about extending
classes. Extending enums just happend to be included in my earlier
message. :-)

Of course, the same undefined situation happens if we allow extending

// Enum3+extra.h
extend class MyThread2 : public MyThread1 {
 extend enum ThreadState { YET_ANOTHER_EXTRA_STATE };

....and if friends extend enums
// ThreadManager.h
class ThreadManager {
  typedef typename Thread::ThreadState ThreadState;
 extend enum ThreadState { SCHEDULED };

...and if we use another design pattern
class Thread;
class WorkerThread {
 Thread *thread;
 typedef typename Thread::ThreadState ThreadState;
 extend enum ThreadState { YET_ANOTHER_STATE_AGAIN };

However, extending classes feels like the next step in creating
reusable code.

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