IEnumerator

Question

I wish to know what this program is try to say.

using System;
using System.Collections;

class MainClass
{
static void Main()
{
int[] intArray = { 10, 11, 12, 13 };

IEnumerator ie = intArray.GetEnumerator();

while (ie.MoveNext() == true)
{
int i = (int)ie.Current;
Console.WriteLine("{0}", i);
}

Console.Read();
}
}
/*
10
11
12
13
*/

Vulpes · Answer

The program is probably trying to show you how the 'foreach' statement works under the hood by using an IEnumerator directly. If you replace all this code: IEnumerator ie = intArray.GetEnumerator(); while (ie.MoveNext() == true) { int i = (int)ie.Current; Console.WriteLine("{0}", i); } with: foreach(int i in intArray) { Console.WriteLine("{0}", i); } the output will be exactly the same.

Maha · Answer

Thanks

Vulpes · Answer

I'll try but there's actually quite a lot going on under the surface with these lines. IEnumerator.Current is of type object but actually returns a 'boxed' int in this particular example as we're dealing with a collection of ints. To unbox the int, you need to cast it to its actual type which is what this line is doing: int i = (int)ie.Current; Console.WriteLine has many overloads and this line: Console.WriteLine("{0}", i); is actually using this overload: Console.WriteLine(string, object); So 'i' is boxed again and the method then prints the object's string representation to the console. If we now consider the line: Console.WriteLine("{0} ", ie.Current); the same overload of Console.WriteLine is called as before but this time there is no further boxing because ie.Current is already of type object. Again the method prints the object's string representation to the console. Note that to obtain the object's string representation, Console.WriteLine() internally calls object's ToString method. As this is a virtual method, it's actually Int32's override which gets called (because this is the actual type of the object in both cases) and so the integer itself gets printed to the console and not its type which object.ToString prints by default.

Maha · Answer

If you replace this int i = (int)ie.Current; Console.WriteLine("{0}", i); with this Console.WriteLine("{0} ", ie.Current); Casting is not necessary. Please explain why?

Maha · Answer

Thanks