Re: Different Objects in Array

From:
Victor Bazarov <v.Abazarov@comAcast.net>
Newsgroups:
comp.lang.c++
Date:
Thu, 07 Jan 2010 21:21:38 -0500
Message-ID:
<hi64rl$7bd$1@news.datemas.de>
Immortal Nephi wrote:

     I thought that you might find an interesting code. Perhaps, you have
seen this before. I created two classes of A and B. Two classes have
different objects. The class Obj has a relationship to class A and
class B which is called composition.
    The class Obj has one variable which is a pointer to member function
in array. You can't bind member function of both class A and class B
because they do not belong to class Obj. I use reinterpret_cast to
convert from class A to class Obj before pointer to member function is
invoked.
    I believe that my code is the alternative replacement so I don't use
inheritance and polymorphism. It is easier to extract class. What do
you think?


Your code has undefined behaviour, not to mention that the compiler that
is supposed to compile your 'reinterpret_cast' will exhibit undefined
behaviour (most likely). Aside from that, you're good...

For example:

class A
{
public:
    A() : x( 10 ) {}
    ~A() {}

    void Run() { x++; cout << "A: " << x << endl; }

private:
    int x;
};

class B
{
public:
    B() : y( 20 ) {}
    ~B() {}

    void Run() { y++; cout << "B: " << y << endl; }

private:
    int y;
};

class Obj
{
public:
    Obj() {}
    ~Obj() {}

    void Run()
    {
        ( this->*pO[0] )();
        ( this->*pO[1] )();
    }

private:
    A a;
    B b;
    typedef void ( Obj::*To )();
    static To const pO[2];
};

Obj::To const Obj::pO[2] =
{
    reinterpret_cast< To >( &A::Run ),
    reinterpret_cast< To >( &B::Run )
};

int main()
{
    Obj o;
    o.Run();

    return 0;
}


V
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