Interview question - C#, multiple inheritance, interfaces

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Hello All,

Recently i was asked a question in one of the interviews:

There is a dll, which has 2 classes

C#

Class A
{
Method A(){...}
}

Class B
{
Method B(){...}
}

In a separate program there is another Class C
Now how can i inherit both CLass B & A in Class C, without modifying anything in the dll?

So how to achieve this?
Please help me in getting the answer to this silly question.

What I have tried:

As multiple inheritance is not supported in C# so I cannot give Class C:B,A
And as i cannot modify anything in the dll, i cannot implement interfaces too..

Posted 13-Jul-16 21:08pm

dinesh_redhawk

Updated 13-Jul-16 23:13pm

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2 solutions

Solution 1

Depends.
You could say: not at all, as multiple inheritance does not exist in C#.
You could say: let's use some tricks. Like that:

C#

Interface IA
{
    Method A();
}
Interface IB
{
    Method B();
}

Then let's add some wrappers which implement the interfaces and just pass thru to the original classes:

C#

class AWrapper : IA
{
    A _Instance;
    AWrapper()
    {
        _Instance = new A();
    }

    Method A ()
    {
        _Instance.A();
    }
}

and similar for B.
Now we can change C:

C#

class C: IA, IB
{
    IA _AInstance;
    IB _BInstance;
    C()
    {
        _AInstance = new AWrapper();
        _BInstance = new BWrapper();
    }

    Method A()
    {
        _AInstance.A();
    }

    Method B()
    {
        _BInstance.B();
    }
}

Well, not exactly inheritance, rather aggregation.

Posted 13-Jul-16 22:20pm

Bernhard Hiller

Comments

[no name] 15-Jul-16 5:12am

the trick which you suggested, i told the same thing but he simply rejected it saying no you cant modify anything in the dll. So, i left with no options..

For this mere question, he rejected me despite me saying that its not possible. :(

Bernhard Hiller 18-Jul-16 3:23am

That doesn't modify anything in the external dll. So: be glad he rejected you so quickly, that's better than to learn later that he's a moron...

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F-ES Sitecore · Accepted Answer · 2016-07-13T23:13:00

Solution 2

My answer would be that you can't. Some interviewers will ask you these kinds of questions to test your confidence and see if you have genuine knowledge or are just trying to game the interview process.

Posted 13-Jul-16 23:13pm

F-ES Sitecore