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From:	"Traveler" <traveler AT netti DOT fi>
Newsgroups:	comp.lang.c++,comp.lang.c++.moderated,comp.os.msdos.djgpp
Subject:	Heterogenous object container without templates & type casting ???
Date:	12 Feb 2002 03:50:10 -0500
Organization:	SAUNALAHDEN asiakas
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Sender:	cppmods AT netlab DOT cs DOT rpi DOT edu
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

Hi

Is it possible to transform the following C code to C++ so that there is no
need for type-casting ?
I am trying to make a general object class that can contain any type without
the use of templates.


#include <stdio.h>
#include <stdlib.h>

typedef struct  A
{
        void*   _p;
        void* (*get)(struct A* this);
}     A;

typedef struct
{
        int*  (*get)(A* this);
} B;


typedef struct
{
        double* (*get)(A* this);
} C;

typedef struct
{
        char*   (*get)(A* this);
} D;

void*   get1(A* this) {return this->_p;}
int*    get2(A* this) {return this->_p;}
double* get3(A* this) {return this->_p;}
char*   get4(A* this) {return this->_p;}

int     main(int argc,char* argv[])
{
        int     value = 66;
        A       a = {&value,get1};    // Simple & dangerous way to "put"
something in to void pointer "a._p"
                                                    // because I had no
patience to play games with "malloc" in this case.......
        B       b = {get2};            // Takes care of the type casting....
        C       c = {get3};
        D       d = {get4};

        printf("I am of type \"int\". My value is %i\n",*b.get(&a));
        printf("I am of type \"double\". My value is %d\n",*c.get(&a));
        printf("I am of type \"char\". My value is %c\n",*d.get(&a));

        return(0);
}


Traveler
traveler AT netti DOT fi




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