Question

I had a class like this

public class Child
{
    public string ToXml()
    {
        return "Child : ToXml()";
    }

    public string ToXml( params string[] fields )
    {
        return "Child : ToXml(...)";
    }
}

creating an instances of class Child and calling ToXml() returns the first overloaded function which was fine and dandy.

var obj = new Child();
Console.WriteLine( obj.ToXml() );

Output:

Child : ToXml()

But when I added a Parent class and changed the Child class to this :

public class Parent
{
    public virtual string ToXml()
    {
        return "Parent : ToXml()";
    }
}

public class Child : Parent
{
    public override string ToXml()
    {
        return "Child : ToXml()";
    }

    public string ToXml( params string[] fields )
    {
        return "Child : ToXml(...)";
    }
}

The output has changed to this :

Child : ToXml(...)

My question is, why is the behaviour like this? (I’m using VS2010 using .NET 3.5)

I kind of ‘fixed’ this problem by changing the second overloaded function to this : (I took out the params keyword

public class Child : Parent
{
    public override string ToXml()
    {
        return "Child : ToXml()";
    }

    public string ToXml( string[] fields )
    {
        return "Child : ToXml(...)";
    }
}

Which brings me to my second question (let me know if I should split this to 2 different post), what is the difference between the functions

ToXml( params string[] fields )

and

ToXml( string[] fields )

They both seems to work when I call the functions like so :

var obj = new Child();
Console.WriteLine( obj.ToXml( new [] { "foo", "bar" ) );

Answer 1

For your first question, this is by design:

For example, the set of candidates for a method invocation does not include methods marked override (Section 7.3), and methods in a base class are not candidates if any method in a derived class is applicable (Section 7.5.5.1).

For your second question, a params modifier make that parameter act as a varargs parameter, meaning it can receive multiple parameters comma-separated, and the array is created implicitly by the compiler.