oop inheritance graph

[a]

Hi,
I have an oop inheritance graph problem.
What is the difference betweent the following 2 inheritance graph?
How does the C++ solve the naming conflict problem for multiple inheritance
problem?

Thanks

A
/ \
B C
\ /
D


A A
| |
B C
\ /
D

 

[aaragon]

Hi,
I have an oop inheritance graph problem.
What is the difference betweent the following 2 inheritance graph?
How does the C++ solve the naming conflict problem for multiple inheritance
problem?

Thanks

A
/ \
B C
\ /
D

A A
| |
B C
\ /
D

There is no difference between the two graphs that you draw since both
B and C inherit from A in both graphs. You have to use "virtual
inheritance" for class A. Scott Meyers discusses this point in detail
in his book Effective C++ (item 43). You may want to avoid this kind
of inheritance graph. The naming convention is defined by the closest
definition of a function to D. For example, if A defines foo() and
this is redefined in C, D uses the C version of foo(). Hope it helps.

 

[Sumit Rajan]

Hi,
I have an oop inheritance graph problem.
What is the difference betweent the following 2 inheritance graph?
How does the C++ solve the naming conflict problem for multiple inheritance
problem?

Thanks

A
/ \
B C
\ /
D


A A
| |
B C
\ /
D

Please see:
http://www.parashift.com/c++-faq-lite/multiple-inheritance.html

 

[James Kanze]

I have an oop inheritance graph problem.
What is the difference betweent the following 2 inheritance graph?
How does the C++ solve the naming conflict problem for multiple inheritance
problem?

A
/ \
B C
\ /
D

A A
| |
B C
\ /
D

In the first, you only have a single instance of A; both B and C
have the same instance as their base class. In the second, you
have two instances. In C++, you use virtual inheritance to
achieve the first, e.g.:

First:

class A {} ;
class B : public virtual A {} ;
class C : public virtual A {} ;
class D : public B, public C {} ;

Second:

class A {} ;
class B : public A {} ;
class C : public A {} ;
class D : public B, public C {} ;

Note the presence of the keyword "virtual" in the inheritance in
the first.

I'm not too sure what you mean by "naming conflict". In the
first, there is only one instance of each class, so there is no
ambituity when referring to a base class. In the second, in D
(or when using an object of type D), any direct reference to A
is ambiguous, since the compiler doesn't know which one; to
disabmiguate, first refer to B or C, e.g. B::A::... or C::A::...

 

[Pete Becker]

There is no difference between the two graphs that you draw since both
B and C inherit from A in both graphs. You have to use "virtual
inheritance" for class A. Scott Meyers discusses this point in detail
in his book Effective C++ (item 43). You may want to avoid this kind
of inheritance graph. The naming convention is defined by the closest
definition of a function to D. For example, if A defines foo() and
this is redefined in C, D uses the C version of foo(). Hope it helps.

No, you don't "have to" use virtual inheritance. That's the difference
between them: the top one uses it and the bottom one doesn't.

--

-- Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com)
Author of "The Standard C++ Library Extensions: a Tutorial and
Reference." (www.petebecker.com/tr1book)

 

[a]

"James Kanze" <[email protected]>
???????:[email protected]...

I have an oop inheritance graph problem.
What is the difference betweent the following 2 inheritance graph?
How does the C++ solve the naming conflict problem for multiple inheritance

A
/ \
B C
\ /
D

A A
| |
B C
\ /
D

In the first, you only have a single instance of A; both B and C
have the same instance as their base class. In the second, you
have two instances. In C++, you use virtual inheritance to
achieve the first, e.g.:

First:

class A {} ;
class B : public virtual A {} ;
class C : public virtual A {} ;
class D : public B, public C {} ;

Second:

class A {} ;
class B : public A {} ;
class C : public A {} ;
class D : public B, public C {} ;

Note the presence of the keyword "virtual" in the inheritance in
the first.

I'm not too sure what you mean by "naming conflict". In the
first, there is only one instance of each class, so there is no
ambituity when referring to a base class. In the second, in D
(or when using an object of type D), any direct reference to A
is ambiguous, since the compiler doesn't know which one; to
disabmiguate, first refer to B or C, e.g. B::A::... or C::A::...

--
James Kanze (GABI Software, from CAI) email:[email protected]
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

Thank you for your reply.
The naming conflict may occur between B and C, since they both inherited
from A. Both B and C have the properties inherited from A, and they have the
same name. So, naming conflict may occurs. I understand the purpose of the
keyword "virtual". But, in terms of "instance", what is the difference
between class B : public virtual A {} and class B : public A {}?

Thanks

 

[James Kanze]

The naming conflict may occur between B and C, since they both
inherited from A. Both B and C have the properties inherited
from A, and they have the same name. So, naming conflict may
occurs.

By "properties", I presume you mean member variables, or ? And
by conflict, you mean ambiguity. If you use virtual inheritance
(the first schema), then there is no ambiguity, since there is
only one instance of A. If you don't use virtual inheritance,
then you refer to either B::A::memberOfA or C::A::memberOfA, in
order to distinguish.

I understand the purpose of the
keyword "virtual". But, in terms of "instance", what is the difference
between class B : public virtual A {} and class B : public A {}?

For class B alone, none, at least from the user's point of view.
It's only when you start to derive further that virtual
inheritance has an effect. With the virtual inheritance as
above, the class D has exactly one instance of A, and something
like B::A::someMember and C::A::someMember refer to exactly the
same object. Without the virtual inheritance, D will have two
instances of A, one as a sub-object of B, and the other as a
sub-object of C, and B::A::someMember and C::A::someMember will
refer to different objects.