Re: extending c++ classes and enumerations

From:

"perrog@gmail.com" <perrog@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

6 Dec 2006 12:13:26 -0500

Message-ID:

<1165411252.832158.41980@16g2000cwy.googlegroups.com>

Al skrev:

Hi there!

alex wrote:

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

void PrintState(ThreadState state) {
    switch (state) {
    case ERROR: cout << "Error"; break;
    case RUNNING: cout << "Running"; break;
    case TERMINATED: cout << "Terminated"; break;
    default: throw exception("Invalid State.");
    }
}

// enum2.h:
extend enum ThreadState { CANCELLED };

int main() {
    PrintState(CANCELLED); // Prints or throws or what?
    return 0;
}

Well, in this case an exception is thrown. :-)
I've noticed that the GNU implementation of standard C++ headers ios
uses static members for e.g. the open mode. In the thread example, this
would look like
enum _ThreadState { _ERROR = -1, _RUNNING, _TERMINATED };
const static int ERROR = _ERROR;
const static int RUNNING = _RUNNING;
const static int TERMINATED = _TERMINATED;

// enum2.h
enum _ThreadState_Cancelled { _CANCELLED };
const static int CANCELLED = _CANCELLED;

but then the point of using enums vanish (no compile checking).

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