Re: Possible to require overloading of a non-pure method?

Pete Becker <>
Fri, 25 Apr 2008 13:11:14 -0400
On 2008-04-25 12:56:34 -0400, "[rob desbois]" <> said:

On Apr 25, 4:22?pm, Pete Becker <> wrote:

On 2008-04-25 10:59:20 -0400, "[rob desbois]" <> said


On Apr 25, 12:46?pm, Pete Becker <> wrote:

On 2008-04-25 06:40:20 -0400, "[rob desbois]" <> s



Hi all, I have a set of classes which implement the virtual
constructor idiom.

I had a slicing problem which resulted when I forgot to override the
clone() function in a derived class.

Is there something (other than documentation) that I can do to prevent

this from happening again?

Unit testing and code reviews.

Allow me to clarify. I meant is there any language construct which can
enforce this requirement.

A unit test wouldn't have helped -- I'd have had to remember to write
a unit test for the new class's clone() method ensuring that the
returned pointer is castable to a pointer to the new derived type. If
I'd have remembered that I'd have remembered to code the clone method

Unit tests would have helped, if they are written correctly and
reviewed correctly. What you're asking for is a language mechamism to
compensate for a weak development process. Fix the process.

The language, its syntax, and libraries are there to support the
developer and the development process.
Would you suggest that using assert() is a weak development process?


Assuming that you were developing this and made the same basic mistake
that I did here -- forgot to override clone() -- where exactly would
the mistake have been spotted?

In the unit tests.

A correctly written unit test? I forgot to implement clone() so would
likely have forgotten the test for it.
A correctly reviewed unit test? In a team of 2 developers in a small
company developing specialised software, where I have the most
experience, I think it unlikely that it would've been caught.

First, accidental omissions are much more likely to be noticed by
someone who didn't write the code. That's the point of reviews: to get
fresh eyes on the code. Second, overriding clone whenever a class is
derived from Base should be part of the review checklist. So, yes, a
review would almost certainly have caught this error.

Roundhouse Consulting, Ltd. ( Author of "The
Standard C++ Library Extensions: a Tutorial and Reference

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