Re: Avoid Casual Mistakes in Overriding a Pure Virtual Function

From:

Pavel Minaev <int19h@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Sat, 21 Mar 2009 08:15:48 CST

Message-ID:

<4c58bde3-4388-4439-af02-5190b88952e8@d19g2000prh.googlegroups.com>

On Mar 20, 5:52 pm, Zhen Yao <allen....@gmail.com> wrote:

I propose a way to avoid casual mistakes in overriding a pure virtual
function. The detail is as follows:

(copied from my original blog posthttp://tech-allen.blogspot.com/2009/03/avoid-casual-mistakes-in-overr...)

A subtle bug costs (but not wastes, :) me an hour this afternoon.

Here's the whole story (if you're not interested in stories, just
scroll to the end of this post to see the conclusions.:):

I have an abstract class:

class TransactionLog {
  public:
   virtual ~TransactionLog() {}
   virtual bool IsSuccessLogged() const = 0;
   ...

};

And a derived concrete class:

class InMemoryTransactionLog : public TransactionLog {
  public:
   virtual bool IsSucessLogged() {
     ...
   }
   ...

};

This is precisely why I wish C++ had an explicit "override" specifier,
along the lines of C#, or at least something similar.

By the way, I recall there was a proposal some time ago that enabled
explicit overrides with optional renaming - I believe the syntax was
something like:

   virtual bool IsSucessLogged() = TransactionLog::IsSucessLogged;

I haven't seen it for a long time though. What happened to it?

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