How do i correctly implement: two inherited (multiple), same-named,pure virtual methods inside a derived class?

[John]

I'm inheriting from multiple abstract base classes (2 to be exact).
In the inherited class I want to know if I can implement two pure
virtual methods (one from each base class) having the same name?

An example is worth a thousand words (Note: I didn't check syntax but
you will get this gist of it), so here it is ....

class Base1
{
virtual void action() = 0;
};

class Base2
{
virtual void action() = 0;
};

class Derived : public Base1, public Base2
{
/*How the heck do I implement both inherited "action" methods? I filled
in an idea here that I'm working on, but cannot seem to get it to
compile ...
*/
Base1::action() { /* do stuff */; } // does not work
Base2::action() { /* do stuff */; } // ditto
};

???

Thanks.
--John

[Pete Becker]

John wrote:

class Base1
{
virtual void action() = 0;
};

class Base2
{
virtual void action() = 0;
};

class Derived : public Base1, public Base2
{
void action() { /* do stuff */; }
};

--

Pete Becker
Dinkumware, Ltd. (http://www.dinkumware.com)

[Rolf Magnus]

John wrote:

I'm inheriting from multiple abstract base classes (2 to be exact).
In the inherited class I want to know if I can implement two pure
virtual methods (one from each base class) having the same name?

An example is worth a thousand words (Note: I didn't check syntax but
you will get this gist of it), so here it is ....

class Base1
{
virtual void action() = 0;
};

class Base2
{
virtual void action() = 0;
};

class Derived : public Base1, public Base2
{
/*How the heck do I implement both inherited "action" methods?

Just the same as you do always:

virtual void action() { /* do stuff */ }
I filled in an idea here that I'm working on, but cannot seem to get
it to compile ...
*/
Base1::action() { /* do stuff */; } // does not work
Base2::action() { /* do stuff */; } // ditto
};

???

[Dietmar Kuehl]

Pete Becker <pe********@acm.org> wrote:

John wrote:

class Base1
{
virtual void action() = 0;
};

class Base2
{
virtual void action() = 0;
};

class Derived : public Base1, public Base2
{

void action() { /* do stuff */; }

};

Of course, this implies that the specification for both 'action()' methods
is identical or at least similar. This is not necessarily a given (although,
admittedly, likely for a function returning nothing and taking no parameter).
If both bases have different requirements on the implementation of the
function and/or a different return type, you have to use two auxiliary base
classes, each implementing one of the functions. I don't think that C++ has
a mechanism like e.g. C# which allows specification of the base class when
overriding a virtual function.
--
<mailto:di***********@yahoo.com> <http://www.dietmar-kuehl.de/>
<http://www.contendix.com> - Software Development & Consulting

[JKop]

Dietmar Kuehl posted:

I don't think that C++ has a mechanism like e.g. C# which
allows specification of the base class when overriding a virtual
function.

class Base1 ...

class Base2 ...

class Derived : public Base1, public Base2 ...
int main()
{
Derived o;

o.Blah;

o.Base1::Blah();

o.Base2::Blah();
}
Or:

void Derived::Blah()
{
this->Base1::Blah();
this->Base2::Blah();
}
-JKop

[Dietmar Kuehl]

JKop wrote:

Dietmar Kuehl posted:

I don't think that C++ has a mechanism like e.g. C# which
allows specification of the base class when overriding a virtual
function.

Note my statement: "... when *overriding* a virtual function." I'm aware and
didn't dispute the fact that you can use specification of a base class when
*calling* a virtual function (well, actually, any function).
class Base1 ...
class Base2 ...
class Derived : public Base1, public Base2 ...
int main()
{
Derived o;
o.Blah;
o.Base1::Blah();
o.Base2::Blah();
}
This is, however, calling a virtual function.
void Derived::Blah()
{
this->Base1::Blah();
this->Base2::Blah();
}

OK, this may be overriding a virtual function but you still cannot qualify
which virtual function is overridden which was what I was referring to,
e.g.:

struct Base1 { virtual int f() = 0; };
struct Base2 { virtual double f() = 0; };
struct Derived1: Base1, Base2 {
// how to define 'f()' here?
};
struct Aux1: Base1 { int f() { return 17; } };
struct Aux2: Base2 { double f() { return 3.14; } };
struct Derived2: Aux1, Aux2 {
// no need to define 'f()' here...
};
--
<mailto:di***********@yahoo.com> <http://www.dietmar-kuehl.de/>
<http://www.contendix.com> - Software Development & Consulting

[Alf P. Steinbach]

* Dietmar Kuehl:

I don't think that C++ has
a mechanism like e.g. C# which allows specification of the base class when
overriding a virtual function.

Right. Visual C++ has that as an extension. With some mysterious quirks...

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