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Generics and Arrays (C# Programming Guide)

Updated: May 2010

In C# 2.0 and later, single-dimensional arrays that have a lower bound of zero automatically implement IList<T>. This enables you to create generic methods that can use the same code to iterate through arrays and other collection types. This technique is primarily useful for reading data in collections. The IList<T> interface cannot be used to add or remove elements from an array. An exception will be thrown if you try to call an IList<T> method such as RemoveAt on an array in this context.

The following code example demonstrates how a single generic method that takes an IList<T> input parameter can iterate through both a list and an array, in this case an array of integers.

class Program
{
    static void Main()
    {
        int[] arr = { 0, 1, 2, 3, 4 };
        List<int> list = new List<int>();

        for (int x = 5; x < 10; x++)
        {
            list.Add(x);
        }

        ProcessItems<int>(arr);
        ProcessItems<int>(list);
    }

    static void ProcessItems<T>(IList<T> coll)
    {
        // IsReadOnly returns True for the array and False for the List.
        System.Console.WriteLine
            ("IsReadOnly returns {0} for this collection.",
            coll.IsReadOnly);

        // The following statement causes a run-time exception for the  
        // array, but not for the List. 
        //coll.RemoveAt(4); 

        foreach (T item in coll)
        {
            System.Console.Write(item.ToString() + " ");
        }
        System.Console.WriteLine();
    }
}

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Reason

May 2010

Removed a note at the end of the topic, and added a call to RemoveAt in method ProcessItems.

Customer feedback.

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