Re: C++ Design question

From:

"Martin Bonner" <martinfrompi@yahoo.co.uk>

Newsgroups:

comp.lang.c++.moderated

Date:

15 Jan 2007 12:01:11 -0500

Message-ID:

<1168854935.357798.309520@38g2000cwa.googlegroups.com>

denis_browne@hotmail.com wrote:

Hi All,

I'm making a class which derives(implements) from 5 interfaces:

class myClass: public base1, public base2, public base3,.......

I want to be able to ask from any interface about a pointer to another
interface
What I mean is:

myClass _myImpObj;

base1 *b1 = &_myImpObj;
base *b2 = b1->QueryInterafce("b2");
base *b3 = b2->QueryInterafce("b3");
base *b1N = b3->QueryInterface("b1");

Its is very simialir to COM mechanism.Anyone knows how to implement it?

struct Unknown { virtual Unknown * QueryInterface(std:string if) = 0;
~Unknown(); }
struct base1 : Unknown { ... }
struct base2 : Unknown { ... }
struct base3 : Unknown { ... }

Unknown * myClass::QueryInterface(std:string if)
{
        if (if == "b1") { return (base1*)this; }
        if (if == "b2") { return (base2*)this; }
        if (if == "b3") { return (base3*)this; }
        return null;
}

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