I can not access Count property of the array but through casting to ICollection !

Question

        int[] arr = new int[5];
        Console.WriteLine(arr.Count.ToString());//Compiler Error
        Console.WriteLine(((ICollection)arr).Count.ToString());//works print 5
        Console.WriteLine(arr.Length.ToString());//print 5

Do you have an explanation for that?

Answer 1

Arrays have .Length, not .Count.

But this is available (as an explicit interface implementation ) on ICollection etc.

Essentially, the same as:

interface IFoo
{
    int Foo { get; }
}
class Bar : IFoo
{
    public int Value { get { return 12; } }
    int IFoo.Foo { get { return Value; } } // explicit interface implementation
}

Bar doesn't have public a Foo property - but it is available if you cast to IFoo :

    Bar bar = new Bar();
    Console.WriteLine(bar.Value); // but no Foo
    IFoo foo = bar;
    Console.WriteLine(foo.Foo); // but no Value

Answer 2

While System.Array implement the ICollection interface it doesn't directly expose the Count property. You can see the explicit implementation of ICollection.Count in the MSDN documentation here .

The same applies to IList.Item .

Take look at this Blog entry for more details on explicit and implicit interface implementation: Implicit and Explicit Interface Implementations

Answer 3

Whilst this doesn't answer your question directly , if you are using .NET 3.5 you can include the namespace;

using System.Linq;

which will then allow you to use a Count() method, similar to when casting your int array as an ICollection.

using System.Linq;

int[] arr = new int[5];
int int_count = arr.Count();

You also then have a whole host of nice functions you can use in Linq too :)