How properly inherit from template?

This is a discussion on How properly inherit from template? within the C++ Programming forums, part of the General Programming Boards category; I realize C# or .NET and C++ are different things, but I do like how the .NET framework is laid ...

  1. #16
    C++まいる!Cをこわせ! Elysia's Avatar
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    I realize C# or .NET and C++ are different things, but I do like how the .NET framework is laid out. That is why I like things to be part of classes and not broken out. It also makes me take distance from standard library functions that clearly does things in a bad in my eyes.

    Yes, they're all respected, they've got loads of experience and what they say may be right. I do respect them, but I don't always agree with them.
    I like .NET layout kind of way, but I don't .NET, so I'm mostly re-engineering C++ in my own way of end without breaking C++ concepts.
    Perhaps it can be done, perhaps not, but I'm certainly not going to just give up.

    Oh and about the virtual destructors thing... I'm just thinking "should" is too strong a word. It's not a requirement, it's good practice, therefore it is strongly recommended in my view. Not should and not must.
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    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

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  2. #17
    Cat without Hat CornedBee's Avatar
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    You have a weird definition of "should".
    All the buzzt!
    CornedBee

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  3. #18
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    Quote Originally Posted by CornedBee View Post
    You have a weird definition of "should".
    It's probably because the would should translates (using "trivial" translation) to "skall" in Swedish, but I think the Swedish word is stronger than the English word.

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  4. #19
    Master Apprentice phantomotap's Avatar
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    I'm just thinking "should" is too strong a word.
    Here I was thinking "must" is spot on. If a class may be crafted polymorphically a virtual destruction mechanism must be provided or it is wrong. If, by requiring the use of some sort of factory, you do not disallow construction/allocation, then the mechanism must be provided by a 'virtual' destructor. If you've not fulfilled this your code is broken for any such behavior. (Yes, the STL containers are broken in this aspect; primarily because it lacks separation of interface and implementation.)

    Soma

  5. #20
    C++ Witch laserlight's Avatar
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    Yes, the STL containers are broken in this aspect; primarily because it lacks separation of interface and implementation.
    I had the impression that the standard containers are not broken in this respect; they were simply not designed to be polymorphic base classes.
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  6. #21
    Master Apprentice phantomotap's Avatar
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    I had the impression that the standard containers are not broken in this respect; they were simply not designed to be polymorphic base classes.
    Hmmm...

    In the case of the STL containers, I would say broken, but one might instead stay deficient-by-design. Personally, I can't imagine that none on the committee, the lot of them being very intelligent, ever thought "Hey, I just bet people will try using them polymorphically from a runtime construct because they provide a very nice and consistent interface". (The compile time polymorphisms provided by the STL are... beyond genius.) So, the only possibility to me, they simply failed to get the specification as good as it might have been in the time they had; thus we have a few broken bits here and there. (I blame the lack of time and apparent pressure against templates for virtually all of the bad bits of the specification.) This is, by the by, what I mean by
    "because it lacks separation of interface and implementation".

    Soma
    Last edited by phantomotap; 04-23-2008 at 08:22 AM.

  7. #22
    C++ Witch laserlight's Avatar
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    In the case of the STL containers, I would say broken, but one might instead stay deficient-by-design. Personally, I can't imagine that none on the committee, the lot of them being very intelligent, ever thought "Hey, I just bet people will try using them polymorphically from a runtime construct because they provide a very nice and consistent interface".
    Well...

    "STL is not object oriented. I think that object orientedness is almost as much of a hoax as Artificial Intelligence. I have yet to see an interesting piece of code that comes from these OO people."
    - Stepanov, An Interview with A. Stepanov
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  8. #23
    Master Apprentice phantomotap's Avatar
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    Yes, I've read it. It isn't particularly interesting. From the same interview:

    I find OOP methodologically wrong. It starts with classes.
    Only when you understand them well, can you come up with an interface that will let them work.
    My approach works, theirs does not work. Try to implement a simple thing in the object oriented way, say, max. I do not know how it can be done.
    Code:
    template <class StrictWeakOrdered>
    inline StrictWeakOrdered& max(StrictWeakOrdered& x,
    StrictWeakOrdered& y) {
    return x < y ? y : x;
    }
    template <class StrictWeakOrdered>
    inline const StrictWeakOrdered& max(const StrictWeakOrdered& x,
    const StrictWeakOrdered& y) {
    return x < y ? y : x;
    }
    Inheritance and interfaces don't help. And if they cannot implement max or swap or linear search, what chances do they have to implement really complex stuff?
    All of this adds up to someone trying to sell you something. His "implementation" does nothing but forward to another function which in virtually all cases must be specifically implemented for each class--indeed, many classes require several such functions providing a "strict weak ordering" for several different metrics. In reality, "OOP" is just an umbrella term for a handful of techniques; many of which he makes use of... whether he likes it or not.

    The only thing the article might show, if that is really your view, is that the STL is indeed deficient-by-design. If you say that something deficient-by-design isn't broken... I will not argue with you. (I do, obviously, disagree.)

    Soma

  9. #24
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    Quote Originally Posted by laserlight View Post
    Well...

    "STL is not object oriented. I think that object orientedness is almost as much of a hoax as Artificial Intelligence. I have yet to see an interesting piece of code that comes from these OO people."
    - Stepanov, An Interview with A. Stepanov
    Wow, he's a pretty opinionated guy. :-) I'd like to see a debate between him and say, a Robert Martin or Grady Booch.

  10. #25
    C++ Witch laserlight's Avatar
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    Yes, I've read it. It isn't particularly interesting.
    I think that it is interesting to read what that fellow was thinking of when he designed the STL that was incorporated into the standard library. It also helps to explain why the committee did not turn the STL containers into polymorphic base classes: they had little time by then to properly retrofit the STL in such a way, even if they felt that it was worth it.

    In reality, "OOP" is just an umbrella term for a handful of techniques; many of which he makes use of... whether he likes it or not.
    I agree, and that is why Stepanov ended up designing the STL in the context of an object oriented language. Also, the basis for the STL's generic programming idiom is the iterator pattern, which was formally documented in OO literature around the time he actually designed the STL.

    Wow, he's a pretty opinionated guy. :-) I'd like to see a debate between him and say, a Robert Martin or Grady Booch.
    Or another opinionated fellow, Linus is his first name, who has spoken out against C++ and the STL
    Last edited by laserlight; 04-23-2008 at 09:23 AM.
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  11. #26
    Master Apprentice phantomotap's Avatar
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    It also helps to explain why the committee did not turn the STL containers into polymorphic base classes: they had little time by then to properly retrofit the STL in such a way, even if they felt that it was worth it.
    O_o

    Me from earlier in the evening:

    So, the only possibility to me, they simply failed to get the specification as good as it might have been in the time they had; thus we have a few broken bits here and there.
    Soma

  12. #27
    C++ Witch laserlight's Avatar
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    Me from earlier in the evening:
    You also wrote:
    I blame the lack of time and apparent pressure against templates for virtually all of the bad bits of the specification.
    I am just pointing out that there was pressure against OO too, though from outside the committee, but presumably supported (perhaps ironically) by Stroustrup.

    Still, I am not sure if this is really a case of "they simply failed to get the specification as good as it might have been". After all, even in Java, inheriting from the standard containers is discouraged in favour of composition.
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  13. #28
    Master Apprentice phantomotap's Avatar
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    After all, even in Java, inheriting from the standard containers is discouraged in favour of composition.
    Not really... depending on what you mean by "inheriting". Extending and implementing the interfaces is expected, even encouraged. Inheriting from an implementation, as for example "java.util.hashset" is probably discouraged. I'm fine with that. (This fits in rather nicely with "separation of interface and implementation".)

    Soma

  14. #29
    C++ Witch laserlight's Avatar
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    Not really... depending on what you mean by "inheriting". Extending and implementing the interfaces is expected, even encouraged. Inheriting from an implementation, as for example "java.util.hashset" is probably discouraged.
    Yes, that is what I mean: inheriting from a concrete class, since the C++ standard containers are concrete classes.

    This fits in rather nicely with "separation of interface and implementation".
    I agree.
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  15. #30
    Master Apprentice phantomotap's Avatar
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    O_o

    We certainly seem to have hijacked this thread "most excellently" considering we seem to agree on everything. ^_^

    Soma

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