.NETics: How Generic Collections work inside?

Tuesday, August 28, 2007

How Generic Collections work inside?

public class TypeSafeList<T>
{
    T[] innerArray = new T[0];
    int currentSize = 0;
    int capacity = 0;

    public void Add(T item)
    {
        // see if array needs to be resized
        if (currentSize == capacity)
        {
            // resize array
            capacity = capacity == 0 ? 4 : capacity * 2;  // double capacity
            T[] copy = new T[capacity];    // create newly sized array
            Array.Copy(innerArray, copy, currentSize);  // copy over the array
            innerArray = copy;    // assign innerArray to the new, larger array
        }

        innerArray[currentSize] = item;
        currentSize++;
    }

    public T this[int index]
    {
        get
        {
            if (index < 0  index >= currentSize)
                throw new IndexOutOfRangeException();
            return innerArray[index];
        }
        set
        {
            if (index < 0  index >= currentSize)
                throw new IndexOutOfRangeException();
            innerArray[index] = value;
        }
    }

    public override string ToString()
    {
        string output = string.Empty;
        for (int i = 0; i < currentSize - 1; i++)
            output += innerArray[i] + ", ";

        return output + innerArray[currentSize - 1];
    }
}