Expilicit Interface Method Implementations:

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Hello Sir,

I read about a fact that Explicit interface methods are used so as to avoid boxing and provide compile time safety.

I tried out a code:

SCENARIO 1:
internal struct somevaluetype : IComparable
{

private int32 m_x;
public somevaluetype(Int32 x)
{
m_x = x;

}

public int32 CompareTo(object other)
{

return(m_x - ((somevaluetype)other).m_x); -------------- statement 1

}

}

static void main()
{

somevaluetype v = new somevaluetype(0);
Object o = new Object();
Int32 n = v.CompareTo(v); /// causes boxing
n = v.CompareTo(o); ///program terminates and throws invalid cast exception

Console.Readline();

}

To avoid above 2 situations i tried out the following :

SCENARIO 2:

internal struct somevaluetype : IComparable
{

private int32 m_x;
public somevaluetype(Int32 x)
{
m_x = x;

}

public int32 CompareTo(somevaluetype other)
{

return (m_x - other.m_x);

}

//// i have to complete the contract of IComparable so i need to implement its method so below:

int32 IComparable.CompareTo(Object other)
{

return m_x - ((somevaluetype)other).m_x) ; -------------- statement2

}

}

static void main()
{

somevaluetype v = new somevaluetype(0);
Object o = new Object();
Int32 n = v.CompareTo(v); /// No boxing
n = v.CompareTo(o); ////doesnt compile

Console.Readline();

}

- These 2 scenarios verify that the External interface method implementations are helpful.
- But what is the difference between statement1 and statement2?
- Statement1 causes run time exception and statement2 causes compile time error.
- and why can i not put any access modifier before an explicit interface method?

Posted 29-Aug-13 9:42am

Rahul VB

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Balkrishna Patel · Answer 1 · 2013-09-01T19:58:00

Hello Rahul,

Statement1 :

you are using a directcast inside CompareTo function. its throws invalid cast exception
when argument is not a type of somevaluetype. i think you have to use following.

C#

public int32 CompareTo(object other)
{
    temp = other as somevaluetype;
	if(temp != null)
	   return (m_x - temp.m_x);
    return -1;
}

Statement2 :

IComparable.CompareTo method don't have any access modifiers. so its consider as private method.
you can't call it from out side. due to that following function throws an compile time error.

C#

n = v.CompareTo(o); ////doesnt compile

I have tested and implemented this code in C#.

Think this help.