Virtual constructor

Discussion in 'C++' started by plmanikandan@gmail.com, Mar 14, 2006.

  1. Guest

    Hi,
    I have doubts reg virtual constructor
    what is virtual constructor?
    Is c++ supports virtual constructor?
    Can anybody explain me about virtual constructor?


    Regards,
    Mani
    , Mar 14, 2006
    #1
    1. Advertising

  2. Phlip Guest

    plmanikandan wrote:

    > Can anybody explain me about virtual constructor?


    Raw C++ cannot call a constructor virtually (because a constructor is not
    really a function). There's probably some common design pattern.

    How about you use Google to survey the topic and report back here?

    --
    Phlip
    http://www.greencheese.org/ZeekLand <-- NOT a blog!!!
    Phlip, Mar 14, 2006
    #2
    1. Advertising

  3. al pacino Guest

    hii,
    there is no such thing as virtual constructor in c++, it doesn't make
    sense.
    a constructor IS a function(can be defined explicitly , compiler calls
    it when an object of a
    class is CREATED.)

    A virtual destructor is required to resolve the ambiguity,when a
    derived class object
    is deleted via a base class pointer(a 'derived class' IS A 'base
    class') since compiler
    has to decide what to delete derived object or base object.
    thus declareing the destructor virtual resolves the ambugity.

    concept of virtual constructor doesnt' make sense to me.
    please correct me if nething is out of place here.
    thanks
    al pacino, Mar 14, 2006
    #3
  4. * :
    >
    > I have doubts reg virtual constructor


    Note: "doubt" means you are unsure whether something is true or not, or
    whether a person is truthful or reliable, or not.

    Your usage above is meaningless and probably due to a bad dictionary.


    > what is virtual constructor?


    See the FAQ. Use the FAQ's Google search (it's on the main page of the
    FAQ) to find the phrase "virtual constructor" in the FAQ. Apart from
    that meaning, which has only a peripheral connection to the words
    "virtual" and "constructor" (it's more like a random phrase that for
    some historical reason has acquired a given meaning), the FAQ also
    discusses another more natural meaning; search the FAQ for the phrase
    "Dynamic Binding During Initialization" to find that discussion.


    > Is c++ supports virtual constructor?


    Yes.


    > Can anybody explain me about virtual constructor?


    Yes, see the FAQ.

    Hth.,

    - Alf

    --
    A: Because it messes up the order in which people normally read text.
    Q: Why is it such a bad thing?
    A: Top-posting.
    Q: What is the most annoying thing on usenet and in e-mail?
    Alf P. Steinbach, Mar 14, 2006
    #4
  5. Sunil Varma Guest

    wrote:
    > Hi,
    > I have doubts reg virtual constructor
    > what is virtual constructor?
    > Is c++ supports virtual constructor?
    > Can anybody explain me about virtual constructor?
    >
    >
    > Regards,
    > Mani


    When you make a function virtual that function is binded after the
    object has been created.
    But if you take a constructor it is called at the time of creation of
    the object.
    Constructor cannot be binded after the object is created.
    Sunil Varma, Mar 14, 2006
    #5
  6. al pacino Guest

    dude how can the constructors can be virtual ??
    here is the reference frm bjarne stroustrup's tech. faq:
    http://public.research.att.com/~bs/bs_faq2.html#virtual-ctor

    Alf P. Steinbach wrote:
    > * :
    > >
    > > I have doubts reg virtual constructor

    >
    > Note: "doubt" means you are unsure whether something is true or not, or
    > whether a person is truthful or reliable, or not.
    >
    > Your usage above is meaningless and probably due to a bad dictionary.
    >
    >
    > > what is virtual constructor?

    >
    > See the FAQ. Use the FAQ's Google search (it's on the main page of the
    > FAQ) to find the phrase "virtual constructor" in the FAQ. Apart from
    > that meaning, which has only a peripheral connection to the words
    > "virtual" and "constructor" (it's more like a random phrase that for
    > some historical reason has acquired a given meaning), the FAQ also
    > discusses another more natural meaning; search the FAQ for the phrase
    > "Dynamic Binding During Initialization" to find that discussion.
    >
    >
    > > Is c++ supports virtual constructor?

    >
    > Yes.
    >
    >
    > > Can anybody explain me about virtual constructor?

    >
    > Yes, see the FAQ.
    >
    > Hth.,
    >
    > - Alf
    >
    > --
    > A: Because it messes up the order in which people normally read text.
    > Q: Why is it such a bad thing?
    > A: Top-posting.
    > Q: What is the most annoying thing on usenet and in e-mail?
    al pacino, Mar 14, 2006
    #6
  7. * al pacino:
    > [top-posting]
    > [quoting extranous material]
    > [quoting signature]


    Please don't top-post. Please don't quote irrelevant stuff. See the
    FAQ and Shiva's monthly "Welcome"-posting in this group.

    --
    A: Because it messes up the order in which people normally read text.
    Q: Why is it such a bad thing?
    A: Top-posting.
    Q: What is the most annoying thing on usenet and in e-mail?
    Alf P. Steinbach, Mar 14, 2006
    #7
  8. Kai-Uwe Bux Guest

    al pacino wrote:

    > dude how can the constructors can be virtual ??


    Easy. What is commonly called a "virtual constructor" just happens not to be
    a constructor (like the Holy Roman Empire was neither roman nor holy and it
    is debatable whether it was an empire).

    > here is the reference frm bjarne stroustrup's tech. faq:
    > http://public.research.att.com/~bs/bs_faq2.html#virtual-ctor


    Did you read what he wrote there? I quote from *that* page:

    Techniques for using an indirection when you ask to create an object
    are often referred to as "Virtual constructors". For example, see
    TC++PL3 15.6.2.

    > Alf P. Steinbach wrote:
    >> * :

    [snip]

    And please, don't top-post.


    Best

    Kai-Uwe Bux
    Kai-Uwe Bux, Mar 14, 2006
    #8
  9. Jim Langston Guest

    "Alf P. Steinbach" <> wrote in message
    news:...
    >* :
    >>
    >> I have doubts reg virtual constructor

    >
    > Note: "doubt" means you are unsure whether something is true or not, or
    > whether a person is truthful or reliable, or not.
    >
    > Your usage above is meaningless and probably due to a bad dictionary.


    Actually, it's probably because he's Norweigian and English is not his
    primary language.

    >> what is virtual constructor?

    >
    > See the FAQ. Use the FAQ's Google search (it's on the main page of the
    > FAQ) to find the phrase "virtual constructor" in the FAQ. Apart from that
    > meaning, which has only a peripheral connection to the words "virtual" and
    > "constructor" (it's more like a random phrase that for some historical
    > reason has acquired a given meaning), the FAQ also discusses another more
    > natural meaning; search the FAQ for the phrase "Dynamic Binding During
    > Initialization" to find that discussion.
    >
    >> Is c++ supports virtual constructor?

    >
    > Yes.


    No. From the FAQ 20.8 in part:

    An idiom that allows you to do something that C++ doesn't directly support.

    >> Can anybody explain me about virtual constructor?

    >
    > Yes, see the FAQ.


    Yes, see the FAQ 20.8 You can't have a virtual constructor, but you can
    have something that mimics what a virtual constructor would do.

    Again, FAQ 20.8 in a bigger part:
    You can get the effect of a virtual constructor by a virtual clone() member
    function (for copy constructing), or a virtual create() member function (for
    the default constructor).

    Here is the link to the FAQ 20.8:
    http://www.parashift.com/c -faq-lite/virtual-functions.html#faq-20.8
    Jim Langston, Mar 14, 2006
    #9
  10. * Jim Langston:
    > "Alf P. Steinbach" <> wrote in message
    > news:...
    >> * :
    >>> I have doubts reg virtual constructor

    >> Note: "doubt" means you are unsure whether something is true or not, or
    >> whether a person is truthful or reliable, or not.
    >>
    >> Your usage above is meaningless and probably due to a bad dictionary.

    >
    > Actually, it's probably because he's Norweigian and English is not his
    > primary language.
    >
    >>> what is virtual constructor?

    >> See the FAQ. Use the FAQ's Google search (it's on the main page of the
    >> FAQ) to find the phrase "virtual constructor" in the FAQ. Apart from that
    >> meaning, which has only a peripheral connection to the words "virtual" and
    >> "constructor" (it's more like a random phrase that for some historical
    >> reason has acquired a given meaning), the FAQ also discusses another more
    >> natural meaning; search the FAQ for the phrase "Dynamic Binding During
    >> Initialization" to find that discussion.
    >>
    >>> Is c++ supports virtual constructor?

    >> Yes.

    >
    > No. From the FAQ 20.8 in part:
    >
    > An idiom that allows you to do something that C++ doesn't directly support.
    >
    >>> Can anybody explain me about virtual constructor?

    >> Yes, see the FAQ.

    >
    > Yes, see the FAQ 20.8 You can't have a virtual constructor, but you can
    > have something that mimics what a virtual constructor would do.
    >
    > Again, FAQ 20.8 in a bigger part:
    > You can get the effect of a virtual constructor by a virtual clone() member
    > function (for copy constructing), or a virtual create() member function (for
    > the default constructor).
    >
    > Here is the link to the FAQ 20.8:
    > http://www.parashift.com/c -faq-lite/virtual-functions.html#faq-20.8


    I'm not sure what point (if any) you were trying to make? Confuse the
    newbie, and remove his or her learning experience in searching the FAQ?
    Look how smart I am, I managed to find it in the FAQ?

    Anyway, your unqualified "no" above is incorrect. C++ does indeed
    support all that's needed to implement what's known as a virtual
    constructor, including virtual member functions and function result
    covariance. Note that this does not contradict the FAQ's statement.

    Hth.,

    - Alf

    --
    A: Because it messes up the order in which people normally read text.
    Q: Why is it such a bad thing?
    A: Top-posting.
    Q: What is the most annoying thing on usenet and in e-mail?
    Alf P. Steinbach, Mar 14, 2006
    #10
  11. Jim Langston Guest

    "Alf P. Steinbach" <> wrote in message
    news:...
    >* Jim Langston:
    >> "Alf P. Steinbach" <> wrote in message
    >> news:...
    >>> * :
    >>>> I have doubts reg virtual constructor
    >>> Note: "doubt" means you are unsure whether something is true or not, or
    >>> whether a person is truthful or reliable, or not.
    >>>
    >>> Your usage above is meaningless and probably due to a bad dictionary.

    >>
    >> Actually, it's probably because he's Norweigian and English is not his
    >> primary language.
    >>
    >>>> what is virtual constructor?
    >>> See the FAQ. Use the FAQ's Google search (it's on the main page of the
    >>> FAQ) to find the phrase "virtual constructor" in the FAQ. Apart from
    >>> that meaning, which has only a peripheral connection to the words
    >>> "virtual" and "constructor" (it's more like a random phrase that for
    >>> some historical reason has acquired a given meaning), the FAQ also
    >>> discusses another more natural meaning; search the FAQ for the phrase
    >>> "Dynamic Binding During Initialization" to find that discussion.
    >>>
    >>>> Is c++ supports virtual constructor?
    >>> Yes.

    >>
    >> No. From the FAQ 20.8 in part:
    >>
    >> An idiom that allows you to do something that C++ doesn't directly
    >> support.
    >>
    >>>> Can anybody explain me about virtual constructor?
    >>> Yes, see the FAQ.

    >>
    >> Yes, see the FAQ 20.8 You can't have a virtual constructor, but you can
    >> have something that mimics what a virtual constructor would do.
    >>
    >> Again, FAQ 20.8 in a bigger part:
    >> You can get the effect of a virtual constructor by a virtual clone()
    >> member function (for copy constructing), or a virtual create() member
    >> function (for the default constructor).
    >>
    >> Here is the link to the FAQ 20.8:
    >> http://www.parashift.com/c -faq-lite/virtual-functions.html#faq-20.8

    >
    > I'm not sure what point (if any) you were trying to make? Confuse the
    > newbie, and remove his or her learning experience in searching the FAQ?
    > Look how smart I am, I managed to find it in the FAQ?
    >
    > Anyway, your unqualified "no" above is incorrect. C++ does indeed support
    > all that's needed to implement what's known as a virtual constructor,
    > including virtual member functions and function result covariance. Note
    > that this does not contradict the FAQ's statement.


    I read the OP's question as: I do not know if C++ would allow a virtual
    constructor, but if it did, what would be it's purpose? What would making a
    constructor virtual accomplish?

    Which is why the two part answer. C++ directly does not support a virtual
    constructor. Which is an answer of No. But, you could do what a virtual
    constructor would supposedly do by using a virtual clone() or create()
    member function which is what people think a virtual constructor would do if
    C++ in fact supported it.

    As far as learning experience in searching in the FAQ, I'm sure that 95% of
    the questions asked in this newsgroup could be answered by STFW, if not 100%
    of them.
    Jim Langston, Mar 14, 2006
    #11
  12. al pacino Guest

    hi alf ,

    of course you can simulate 'virtual ' constructor, but there is no
    'direct' support(from compiler) like it is for virtual destructor.
    al pacino, Mar 14, 2006
    #12
  13. * Jim Langston:
    > "Alf P. Steinbach" <> wrote in message
    > news:...
    >> * Jim Langston:
    >>> "Alf P. Steinbach" <> wrote in message
    >>> news:...
    >>>> * :
    >>>>> I have doubts reg virtual constructor
    >>>> Note: "doubt" means you are unsure whether something is true or not, or
    >>>> whether a person is truthful or reliable, or not.
    >>>>
    >>>> Your usage above is meaningless and probably due to a bad dictionary.
    >>> Actually, it's probably because he's Norweigian and English is not his
    >>> primary language.
    >>>
    >>>>> what is virtual constructor?
    >>>> See the FAQ. Use the FAQ's Google search (it's on the main page of the
    >>>> FAQ) to find the phrase "virtual constructor" in the FAQ. Apart from
    >>>> that meaning, which has only a peripheral connection to the words
    >>>> "virtual" and "constructor" (it's more like a random phrase that for
    >>>> some historical reason has acquired a given meaning), the FAQ also
    >>>> discusses another more natural meaning; search the FAQ for the phrase
    >>>> "Dynamic Binding During Initialization" to find that discussion.
    >>>>
    >>>>> Is c++ supports virtual constructor?
    >>>> Yes.
    >>> No. From the FAQ 20.8 in part:
    >>>
    >>> An idiom that allows you to do something that C++ doesn't directly
    >>> support.
    >>>
    >>>>> Can anybody explain me about virtual constructor?
    >>>> Yes, see the FAQ.
    >>> Yes, see the FAQ 20.8 You can't have a virtual constructor, but you can
    >>> have something that mimics what a virtual constructor would do.
    >>>
    >>> Again, FAQ 20.8 in a bigger part:
    >>> You can get the effect of a virtual constructor by a virtual clone()
    >>> member function (for copy constructing), or a virtual create() member
    >>> function (for the default constructor).
    >>>
    >>> Here is the link to the FAQ 20.8:
    >>> http://www.parashift.com/c -faq-lite/virtual-functions.html#faq-20.8

    >> I'm not sure what point (if any) you were trying to make? Confuse the
    >> newbie, and remove his or her learning experience in searching the FAQ?
    >> Look how smart I am, I managed to find it in the FAQ?
    >>
    >> Anyway, your unqualified "no" above is incorrect. C++ does indeed support
    >> all that's needed to implement what's known as a virtual constructor,
    >> including virtual member functions and function result covariance. Note
    >> that this does not contradict the FAQ's statement.

    >
    > I read the OP's question as: I do not know if C++ would allow a virtual
    > constructor, but if it did, what would be it's purpose? What would making a
    > constructor virtual accomplish?


    Don't inform me. Instead, bring your interpretation with your response,
    if it has any bearing on the response. Anyway, I think it's a Good Idea
    to assume a question is meaningful, like the established meaning for the
    actual words used by the OP, rather than something meaningless.


    > Which is why the two part answer. C++ directly does not support a virtual
    > constructor. Which is an answer of No. But, you could do what a virtual
    > constructor would supposedly do by using a virtual clone() or create()
    > member function which is what people think a virtual constructor would do if
    > C++ in fact supported it.


    Also here. There are several possible meanings for "virtual
    constructor" apart from the established meaning, most notably the one of
    doing virtual construction (where part of the construction is specified
    by a derived class; directly supported in Java and C# by breaking those
    languages' type safety, and possible to simulate in C++, see the FAQ).
    But yours isn't one: a constructor can't do the job of a clone function.


    > As far as learning experience in searching in the FAQ, I'm sure that 95% of
    > the questions asked in this newsgroup could be answered by STFW, if not 100%
    > of them.


    Does that mean "Searching The Fucking Web"? Language, Jim. Also,
    that's highly misleading: nobody tried to send anyone on a wild-goose
    chase, as you imply, but instead the OP was directed on a highly focused
    search guaranteed to yield a useful result.

    But you then stepped in with a totally unncessary "clear up things"
    posting which in addition to depriving the OP the chance to learn to
    something, was factually incorrect, and as you now clarify, relied on a
    meaningless interpretation of the question rather than assuming some
    meaning in there.


    --
    A: Because it messes up the order in which people normally read text.
    Q: Why is it such a bad thing?
    A: Top-posting.
    Q: What is the most annoying thing on usenet and in e-mail?
    Alf P. Steinbach, Mar 14, 2006
    #13
  14. * al pacino:
    > hi alf ,
    >
    > of course you can simulate 'virtual ' constructor, but there is no
    > 'direct' support(from compiler) like it is for virtual destructor.


    It /is/ possible to quote using Google groups, but I think you have to
    press some button or some such (please check that out).

    Anyway, there's no need to "simulate" a "virtual" constructor.

    The phrase "virtual constructor" has an established meaning, and can be
    expressed directly in C++ without any simulation at all; see the FAQ.

    --
    A: Because it messes up the order in which people normally read text.
    Q: Why is it such a bad thing?
    A: Top-posting.
    Q: What is the most annoying thing on usenet and in e-mail?
    Alf P. Steinbach, Mar 14, 2006
    #14
  15. Rolf Magnus Guest

    Alf P. Steinbach wrote:

    >> I read the OP's question as: I do not know if C++ would allow a virtual
    >> constructor, but if it did, what would be it's purpose? What would
    >> making a constructor virtual accomplish?

    >
    > Don't inform me. Instead, bring your interpretation with your response,
    > if it has any bearing on the response. Anyway, I think it's a Good Idea
    > to assume a question is meaningful, like the established meaning for the
    > actual words used by the OP, rather than something meaningless.
    >
    >
    >> Which is why the two part answer. C++ directly does not support a
    >> virtual constructor. Which is an answer of No. But, you could do what a
    >> virtual constructor would supposedly do by using a virtual clone() or
    >> create() member function which is what people think a virtual constructor
    >> would do if C++ in fact supported it.

    >
    > Also here. There are several possible meanings for "virtual constructor"
    > apart from the established meaning,


    Those other meanings are based on incorrect interpretations of the word
    "virtual". The GoF book calls it "factory method", which is a much better
    name for it.

    > most notably the one of doing virtual construction (where part of the
    > construction is specified by a derived class; directly supported in Java
    > and C# by breaking those languages' type safety, and possible to simulate
    > in C++, see the FAQ).
    > But yours isn't one: a constructor can't do the job of a clone function.


    A constructor can't do the job of a "virtual constructor" either. What the
    FAQ mentions is not a constructor or something that does the job of a
    constructor. The clone() function would even be closer to something like a
    virtual constructor than a factory, because it can at least take the
    dynamic type of an existing object, as virtual functions do. A factory
    needs some other means to decide with class to instantiate.

    >> As far as learning experience in searching in the FAQ, I'm sure that 95%
    >> of the questions asked in this newsgroup could be answered by STFW, if
    >> not 100% of them.

    >
    > Does that mean "Searching The Fucking Web"? Language, Jim.


    You were the one who used the word.

    > Also, that's highly misleading: nobody tried to send anyone on a
    > wild-goose chase, as you imply, but instead the OP was directed on a
    > highly focused search guaranteed to yield a useful result.
    >
    > But you then stepped in with a totally unncessary "clear up things"
    > posting


    Clearing things up is not unnecessary, especially not in a technical forum.

    > which in addition to depriving the OP the chance to learn to something,
    > was factually incorrect,


    It was correct.

    > and as you now clarify, relied on a meaningless interpretation of the
    > question rather than assuming some meaning in there.


    The C++ standard's definition of the word "virtual" is not at all
    meaningless in a C++ newsgroup.
    Rolf Magnus, Mar 14, 2006
    #15
  16. * Rolf Magnus:
    > Alf P. Steinbach wrote:
    >
    >>> I read the OP's question as: I do not know if C++ would allow a virtual
    >>> constructor, but if it did, what would be it's purpose? What would
    >>> making a constructor virtual accomplish?

    >> Don't inform me. Instead, bring your interpretation with your response,
    >> if it has any bearing on the response. Anyway, I think it's a Good Idea
    >> to assume a question is meaningful, like the established meaning for the
    >> actual words used by the OP, rather than something meaningless.
    >>
    >>
    >>> Which is why the two part answer. C++ directly does not support a
    >>> virtual constructor. Which is an answer of No. But, you could do what a
    >>> virtual constructor would supposedly do by using a virtual clone() or
    >>> create() member function which is what people think a virtual constructor
    >>> would do if C++ in fact supported it.

    >> Also here. There are several possible meanings for "virtual constructor"
    >> apart from the established meaning,

    >
    > Those other meanings are based on incorrect interpretations of the word
    > "virtual".


    Nope, sorry, that's incorrect.


    > The GoF book calls it "factory method", which is a much better name for it.


    The GoF book calls /what/ the "factory method"?

    Anyway, qualified names are good, so now we can speak of "GOF factory
    method", as soon as we've checked that it's at all relevant.


    >> most notably the one of doing virtual construction (where part of the
    >> construction is specified by a derived class; directly supported in Java
    >> and C# by breaking those languages' type safety, and possible to simulate
    >> in C++, see the FAQ).
    >> But yours isn't one: a constructor can't do the job of a clone function.

    >
    > A constructor can't do the job of a "virtual constructor" either.


    A "virtual constructor" /is/ a clone function, in the established
    meaning; see the FAQ.


    > What the
    > FAQ mentions is not a constructor or something that does the job of a
    > constructor. The clone() function would even be closer to something like a
    > virtual constructor than a factory, because it can at least take the
    > dynamic type of an existing object, as virtual functions do. A factory
    > needs some other means to decide with class to instantiate.


    The FAQ mentions several things.

    What on Earth are you, uh, /talking/ about?


    >>> As far as learning experience in searching in the FAQ, I'm sure that 95%
    >>> of the questions asked in this newsgroup could be answered by STFW, if
    >>> not 100% of them.

    >> Does that mean "Searching The Fucking Web"? Language, Jim.

    >
    > You were the one who used the word.


    That's a lie.


    >> Also, that's highly misleading: nobody tried to send anyone on a
    >> wild-goose chase, as you imply, but instead the OP was directed on a
    >> highly focused search guaranteed to yield a useful result.
    >>
    >> But you then stepped in with a totally unncessary "clear up things"
    >> posting

    >
    > Clearing things up is not unnecessary, especially not in a technical forum.


    Confusing things is.



    >> which in addition to depriving the OP the chance to learn to something,
    >> was factually incorrect,

    >
    > It was correct.


    Nope, sorry, you're incorrect.


    >> and as you now clarify, relied on a meaningless interpretation of the
    >> question rather than assuming some meaning in there.

    >
    > The C++ standard's definition of the word "virtual" is not at all
    > meaningless in a C++ newsgroup.


    What are you babbling about?



    --
    A: Because it messes up the order in which people normally read text.
    Q: Why is it such a bad thing?
    A: Top-posting.
    Q: What is the most annoying thing on usenet and in e-mail?
    Alf P. Steinbach, Mar 14, 2006
    #16
  17. Rolf Magnus Guest

    Alf P. Steinbach wrote:

    > * Rolf Magnus:
    >> Alf P. Steinbach wrote:
    >>
    >>>> I read the OP's question as: I do not know if C++ would allow a virtual
    >>>> constructor, but if it did, what would be it's purpose? What would
    >>>> making a constructor virtual accomplish?
    >>> Don't inform me. Instead, bring your interpretation with your response,
    >>> if it has any bearing on the response. Anyway, I think it's a Good Idea
    >>> to assume a question is meaningful, like the established meaning for the
    >>> actual words used by the OP, rather than something meaningless.
    >>>
    >>>
    >>>> Which is why the two part answer. C++ directly does not support a
    >>>> virtual constructor. Which is an answer of No. But, you could do what
    >>>> a virtual constructor would supposedly do by using a virtual clone() or
    >>>> create() member function which is what people think a virtual
    >>>> constructor would do if C++ in fact supported it.
    >>> Also here. There are several possible meanings for "virtual
    >>> constructor" apart from the established meaning,

    >>
    >> Those other meanings are based on incorrect interpretations of the word
    >> "virtual".

    >
    > Nope, sorry, that's incorrect.
    >
    >
    >> The GoF book calls it "factory method", which is a much better name for
    >> it.

    >
    > The GoF book calls /what/ the "factory method"?


    Under the description of "factory method", it says "also known as virtual
    constructor". And while we're at it, from TC++PL:
    <refering to a factory class>
    "Such a class is sometimes called a factory, and its functions are (somewhat
    misleadingly) sometimes called virtual constructors.

    I thought that was what you meant by "virtual constructor", which seems to
    be not the case.

    > Anyway, qualified names are good, so now we can speak of "GOF factory
    > method", as soon as we've checked that it's at all relevant.


    Well, we could also call it the Steinbach virtual constructor then.

    >>> most notably the one of doing virtual construction (where part of the
    >>> construction is specified by a derived class; directly supported in Java
    >>> and C# by breaking those languages' type safety, and possible to
    >>> simulate in C++, see the FAQ).
    >>> But yours isn't one: a constructor can't do the job of a clone function.

    >>
    >> A constructor can't do the job of a "virtual constructor" either.

    >
    > A "virtual constructor" /is/ a clone function, in the established
    > meaning; see the FAQ.


    What makes you think that the FAQ represents "the established meanging"?
    Anyway, I have to admit that I didn't look at the FAQ's explanations of
    "virtual constructor", because I thought it must be the same as what the
    GoF and Stroustrup say. Considering that it actually isn't, the meaning
    described in the FAQ doesn't seem so well-established after all, does it?

    >> What the
    >> FAQ mentions is not a constructor or something that does the job of a
    >> constructor. The clone() function would even be closer to something like
    >> a virtual constructor than a factory, because it can at least take the
    >> dynamic type of an existing object, as virtual functions do. A factory
    >> needs some other means to decide with class to instantiate.

    >
    > The FAQ mentions several things.
    >
    > What on Earth are you, uh, /talking/ about?


    Sorry, I was talking about another "established meaning" of the term.

    >>>> As far as learning experience in searching in the FAQ, I'm sure that
    >>>> 95% of the questions asked in this newsgroup could be answered by STFW,
    >>>> if not 100% of them.
    >>> Does that mean "Searching The Fucking Web"? Language, Jim.

    >>
    >> You were the one who used the word.

    >
    > That's a lie.


    At least you show some humor :)

    >>> Also, that's highly misleading: nobody tried to send anyone on a
    >>> wild-goose chase, as you imply, but instead the OP was directed on a
    >>> highly focused search guaranteed to yield a useful result.
    >>>
    >>> But you then stepped in with a totally unncessary "clear up things"
    >>> posting

    >>
    >> Clearing things up is not unnecessary, especially not in a technical
    >> forum.

    >
    > Confusing things is.


    Then stop doing that.

    >>> which in addition to depriving the OP the chance to learn to something,
    >>> was factually incorrect,

    >>
    >> It was correct.

    >
    > Nope, sorry, you're incorrect.


    From the C++ standard: "A constructor shall not be virtual". Whatever some
    other definition (be it established or not) says is irelevant.

    >>> and as you now clarify, relied on a meaningless interpretation of the
    >>> question rather than assuming some meaning in there.

    >>
    >> The C++ standard's definition of the word "virtual" is not at all
    >> meaningless in a C++ newsgroup.

    >
    > What are you babbling about?


    Jim was interpreting the term according to the C++ standard ("you can't have
    a virtual constructor"), and you called that interpretation meaningless.
    Rolf Magnus, Mar 14, 2006
    #17
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. Giulio
    Replies:
    9
    Views:
    1,040
    Patrick Kowalzick
    Jun 25, 2003
  2. Brett Irving
    Replies:
    3
    Views:
    3,330
    John Harrison
    Jun 29, 2003
  3. lallous
    Replies:
    5
    Views:
    8,815
    David Harmon
    Jan 23, 2004
  4. Aire
    Replies:
    3
    Views:
    462
    Mike Wahler
    Jan 25, 2004
  5. Generic Usenet Account
    Replies:
    10
    Views:
    2,217
Loading...

Share This Page