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From: "Traveler" <traveler AT netti DOT fi>
Newsgroups: comp.lang.c++,comp.lang.c++.moderated,comp.os.msdos.djgpp
Subject: Re: Heterogenous object container without templates & type casting ???
Date: 13 Feb 2002 16:35:05 -0500
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"rb" <rbinion AT rcn DOT com> kirjoitti viestissä
news:a4a7ii$9qv$1 AT bob DOT news DOT rcn DOT net...

Thanks for your answer !

> 5. I am probably missing the overall gist of what you are trying to do.
But
> if you want the _p member of struct A to be accesible as an int, double
and
> char .. wouldn't you be better of just using a union?

Could you send me the union version of the code allso ?

>
> 6. Finaly here is roughly the equivalent C++ code with templates. Note I
> used the c io routines rather than the C++ iostreams so as not to further
> complicate the issue, made everything public for the same reason, and also
> left out other C++ idioms (like using const, ctor's, etc.).
>
> template<typename T> class holder
> {
> public:
>     T value_;
> };
>
> int main(int argc,char* argv[])
> {
>  int value = 66;
>
>  holder<int> b = {value};
>  holder<double> c = {value};
>  holder<char> d = {value};
>
>  printf("I am of type \"int\". My value is %i\n",(b.value_));
> printf("I am of type \"double\". My value is %f\n",(c.value_));
> printf("I am of type \"char\". My value is %c\n",(d.value_));
>
>  return 0;
> }
>
>

Yeah, thats exactly what I thought people would send to me except that
there´s no constructor's & cout.
Anyway, my "great" project is to do something like this...


class    Trivial : public Object
{
    double    _x;
    double    _y;
public:
    Trivial():_x(10),_y(20) {}
    double    getX()const {return    this->_x;}
    double    getY()const {return    this->_y;}
    friend    ostream&    operator<<(ostream& stream,const Trivial& src)
    {
        stream << "x:\t" << src._x << "\ty:" << src._y;
        return    stream;
    }
};

int    main(int argc,char* argv[])
{
    List<Object>    myList;

    myList.appendEnd('A');                // "Index" position 0
    myList.appendEnd(55);                // 1
    myList.appendEnd(-32.123);      // etc...
    myList.appendEnd(Trivial());

    cout << myList.first()->data() << endl;        // prints "A"
    myList.remove(myList.first());
    cout << myList.first()->data() << endl;        // prints 55
    myList.remove(myList.first());
    cout << myList.first()->data() << endl;        // prints -32.123
    myList.remove(myList.first());
    cout << myList.first()->data() << endl;        // prints x: 10    y: 20
    return(0);
}

As you can see this is heterogenic list !

It is supposed that :
A)    function    "myList.appendEnd" is:
template <typename Type>
List<Type>::Node*    List<Type>::appendEnd(const Type& data)
{
.....
}

B)    function "first()" is declared like this:
template <typename Type>
List<Type>::Node*    List<Type>::first()const
{
    return    this->_first;
}

C) function "data()" is declared like this:
Object&    List<Type>::Node::data()const        // Not that it is the
"Nodes" responsibility to return the data
{
    return    this->_data;
}

As you can see there is this thing "List<Object>    myList" and this is
exactly where we get into the subject.
I need a heterogenous object container WITHOUT the use of templates so that
I can declare a heterogenous list like above.

Note allso that there is no typecasting in the part of "cout <<
myList.first()->data() << endl" in the imaginary code.

So, if you have any advise how to accomplish this, please, maill immediately
to me

Thanks !!!
Traveler
traveler AT netti DOT fi





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