Re: inheriting from std::vector bad practice?

From:
"Alf P. Steinbach" <alfps@start.no>
Newsgroups:
comp.lang.c++
Date:
Sat, 03 Apr 2010 18:16:44 +0200
Message-ID:
<hp7poq$ae2$1@news.eternal-september.org>
* Leigh Johnston:

"Alf P. Steinbach" <alfps@start.no> wrote in message
news:hp7p5m$6rb$1@news.eternal-september.org...

* Leigh Johnston:

* Alf P. Steinbach:

* Leigh Johnston:

The only time it is unwise to use public inheritance is if your
class invariant consists of more than just vector's invariant in
which case it might be possible to break your class's invariant by
calling the vector's member functions, but I don't believe this is
the case in your example (i.e. you are simply performing interface
augmentation).


Sorry, that's bullshit. Proper design involves much more. It's
possible to disagree over what constitutes a good design and whether
something constitutes good design, but in this case it's about the
opposite, a technique that's almost universally recognized as
Bad(TM), so, no discussion.


[don't quote signatures, please, and please /trim/ your quoting]

Sorry but that's bullshit. Interface augmentation is a perfectly
valid design practice.


The OP isn't doing interface augmentation by deriving from
std::vector<Point>.

And that's not what you were talking about, your statement about "the
only time it is unwise to use public inheritance", quoted above.

I.e. you're now attacking a strawman argument or a couple of strawman
arguments.

Instead of inventive strawman argumentation you might reasonably and
straigtforwardly ask why, according to me, your earlier statement is
commonly regarded as bullshit.

As opposed to strawman argumentation, which usually leads to negative
outcomes, such questioning might prove the label-affixer (i.e. here
me) wrong, or you could learn something, or whatever, but mostly
positive outcomes from asking.

Cheers & hth.,

- Alf


You are simply full of shit. Hope this helps.


Assume that you're right about my bodily contents. Does that help your argument?

No, it does not: it is a fallacy to attack the person.

Let's mark this up as Fallacy #1.

I repeat: interface augmentation (which is what my reply was referring
to) is quite valid


Sometimes interface augmentation is a good idea, but in this case there is no
interface augmentation. Mentioning interface agumentation is just a strawman
argument, which is a fallacy. Let's mark this up as Fallacy #2.

and Bjarne Stroustrup agrees.


This is just an appeal to authority. Which is a fallacy even when it's done
properly with references. Let's mark this as Fallacy #3.

 The OP is simply
augmenting vector's interface as far as I can tell (not introducing any
new member variables that contribute to an invariant larger than vector's.)


No. std::vector is a generic type, a template type. The OP is not augmenting
std::vector.

Cheers & hth.,

- Alf

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