Hi,

How to avoid deriving a class to more than one class?
For example consider I have a Class A ( base class) which is derived
by Class B. Now if I try to derive Class A to Class C it shouldn't be
allowed. How can I do this?

class A
{
}
class B:class A
{
}
class C: class A // deriving class A should not be allowed
{
}

Thanks in advance for your help.

You could put something together that prevents you creating instances of
more than one derived class at runtime. I can't think of a way to stop
you writing more than one derived class.

The main question, though, is why on earth have you got this
requirement? Methinks your design is probably (very) wrong..



On 06/07/2011 08:01, VijayRama wrote:
> Hi,
>
> How to avoid deriving a class to more than one class?
> For example consider I have a Class A ( base class) which is derived
> by Class B. Now if I try to derive Class A to Class C it shouldn't be
> allowed. How can I do this?
>
> class A
> {
> }
> class B:class A
> {
> }
> class C: class A // deriving class A should not be allowed
> {
> }
>
> Thanks in advance for your help.
>

On Jul 6, 10:01*am, VijayRama <vijay3...@gmail.com> wrote:
> Hi,
>
> How to avoid deriving a class to more than one class?
> For example consider I have a Class A ( base class) which is derived
> by Class B. Now if I try to derive Class A to Class C it shouldn't be
> allowed. How can I do this?
>
> class A
> {}
>
> class B:class A
> {}
>
> class C: class A // deriving class A should not be allowed
> {
>
> }
>
> Thanks in advance for your help.

The compiler will stop you if your classes are circular.

As for: class C: class A // deriving class A should not be allowed

Just make a mental note not to do that when you code. If you mean
during run time, then simply don't make C depend on A--presto! you
are done.

RL

On 7/7/2011 7:10 AM, RayLopez99 wrote:
> On Jul 6, 10:01 am, VijayRama<vijay3...@gmail.com> wrote:
>> Hi,
>>
>> How to avoid deriving a class to more than one class?
>> For example consider I have a Class A ( base class) which is derived
>> by Class B. Now if I try to derive Class A to Class C it shouldn't be
>> allowed. How can I do this?
>>
>> class A
>> {}
>>
>> class B:class A
>> {}
>>
>> class C: class A // deriving class A should not be allowed
>> {
>>
>> }
>
> The compiler will stop you if your classes are circular.

True, but that is not the case here.

> Just make a mental note not to do that when you code. If you mean
> during run time, then simply don't make C depend on A--presto! you
> are done.

That is a simple solution that may or may not work.

Arne

On 7/6/2011 3:01 AM, VijayRama wrote:
> How to avoid deriving a class to more than one class?
> For example consider I have a Class A ( base class) which is derived
> by Class B. Now if I try to derive Class A to Class C it shouldn't be
> allowed. How can I do this?
>
> class A
> {
> }
> class B:class A
> {
> }
> class C: class A // deriving class A should not be allowed
> {
> }

What is is that you want?

Do you want to prevent more than one type of A to be
instantiated within a running program?

Try a run time check a la:

public class A
{
private static Type sub = null;
public A()
{
if(sub == null)
{
sub = this.GetType();
}
else if(sub != this.GetType())
{
throw new Exception("No no my friend");
}
}
}

Do you want to prevent more than one type to inherit from
a public class A in an assembly?

Can not be done. If I get a copy of that assembly on my PC I can inherit
as much as I want.

Do you want to prevent more than one type to inherit from
an internal class A within the same assembly?

You can not make a compile time check. But you can make a runtime
check similar to the above to prevent instantiation of multiple
subclasses.

Do you have a class that you only want to allow inheritance
from in some specific assemblies?

Make it internal and use the InternalsVisibleToAttribute.

Arne