interface with C-Sharp

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5.00/5 (1 vote)

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C#

Interface is value type or reference type?

please help
i am totally confused.

thanq.

Posted 19-Oct-11 5:29am

sreekanth12

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Sergey Alexandrovich Kryukov 19-Oct-11 12:28pm

Looking simple, this is a very provocative question -- thank you very much, get my 5.
To understand why it's so non-trivial, please see my answer.
--SA

4 solutions

Solution 5

I would add to the basically correct answer by Collin and Mehdi:

Another question is: we declare a variable of interface type, is it of value type reference type?
Interesting question, really. In certain sense, it is always of reference type, because this is a reference to some object. But! For a variable itself only its compile-time type is known, call it "reference to something" if you well. When this variable is assigned to some object, the object could be either reference (in case if implementing type is a class) or value type (in case if implementing type is struct). In case of struct, however, the object is always boxed in a reference type as it appears through the variable of interface type.

A really delicate issue, in a way.

—SA

Posted 19-Oct-11 6:25am

Sergey Alexandrovich Kryukov

Updated 19-Oct-11 6:31am

v2

Comments

Mehdi Gholam 19-Oct-11 12:36pm

I was right afterall! 5!

Sergey Alexandrovich Kryukov 19-Oct-11 12:50pm

Thank you, Mehdi.
Yes, on the after-math, but only because you did not know or did not remember that struct can also implement interfaces. This fact is not well realized by people, and the implication is not trivial; this is actually another kind of polymorphism not based on late binding in the sense of virtual functions (which are not available in struct). Some people explained it to me an year ago or so -- I did not realize it myself. Now, how this is represented via interface reference is not quite trivial.
--SA

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Reiss · Accepted Answer · 2011-10-19T05:37:00

Solution 4

An interface is neither but the implementing type can be either

e.g.

C#

public interface ITest
{
    void DoSomething();
}

public class TestClass : ITest
{
    public void DoSomething()
    {
        
    }
}

public struct TestStruct : ITest
{
    public void DoSomething()
    {
        
    }
}

see MSDN[^] for more details

Posted 19-Oct-11 5:37am

Reiss

Comments

Mehdi Gholam 19-Oct-11 11:45am

my 5!

Sergey Alexandrovich Kryukov 19-Oct-11 12:29pm

I voted 4, because this is not so easy. Please see my solution and my comment to the answer by Collin.
--SA

Uday P.Singh 19-Oct-11 13:04pm

Agree my 5!

RaviRanjanKr 20-Oct-11 3:29am

My 5+

N_tro_P · Accepted Answer · 2011-10-19T05:33:00

Solution 1

Neither. Interface is a contract.

It can be used on either ref or value types.

For example,

C#

public struct CustomIntCollectionValueType : ICollection<int>
{
  //Implementation here
}
</int>

or

C#

public class CustomIntCollectionRefType : ICollection<int>
{
  //Implementation
}
</int>

In this case I am using a system provided interface. One can create their own interface and implement it upon a value type (struct) or ref type (class).

Posted 19-Oct-11 5:33am

N_tro_P

Updated 19-Oct-11 6:17am

v3

Comments

Mehdi Gholam 19-Oct-11 11:46am

my 5!

[no name] 19-Oct-11 11:53am

Thank you :)

Sergey Alexandrovich Kryukov 19-Oct-11 12:19pm

Collin, I fixed you pretty nasty spelling mistake in 3 placed; please learn this word.
--SA

[no name] 19-Oct-11 13:17pm

Thank you. I am a horrible speller, and unfortunately CP offers no help (spell check). Conent was good though :-)

Sergey Alexandrovich Kryukov 19-Oct-11 12:27pm

About your answer, I don't know what to say... This is not so simple. In some sense, interface as a variable of such type is always a reference type, as struct appears in a boxed way. This is such a delicate issue -- please see my solution.
Well... I'll vote 4 I guess...
--SA

[no name] 19-Oct-11 13:19pm

I am a little confused by your answer actually. I am guessing you are saying if one has a variable, lets say a property that is to be injected, it is actually a reference type. And if it turns out the implimentation of the interface that is injected is a struct, then it is a ref type wrapped around a struct. Is this correct?

RaviRanjanKr 20-Oct-11 3:31am

My 5+

Mehdi Gholam · Accepted Answer · 2011-10-19T05:35:00

Solution 3

An interface is an interface, what the underlying object who implemented that interface can be only a reference type as it has to be a class not string, int, ...

EDIT -> I stand corrected, structs can implement interfaces too.

Posted 19-Oct-11 5:35am

Mehdi Gholam

Updated 19-Oct-11 5:45am

v2

Comments

[no name] 19-Oct-11 11:38am

Are you sure about that? I am pretty sure a struct can impliment an interface...

Mehdi Gholam 19-Oct-11 11:43am

Good point, I never used interfaces with structs.

[no name] 19-Oct-11 11:53am

Yeah me neither... But then again I never use structs. I will admit, I had to check :-)

Reiss 19-Oct-11 11:39am

Struct's can implement interfaces too

Mehdi Gholam 19-Oct-11 11:45am

Thanks, updated the solution.

Sergey Alexandrovich Kryukov 19-Oct-11 12:30pm

I voted 4, because this is not so easy. Please see my solution and my comment to the answer by Collin.
--SA