Question

Somebody please shed some light on how Add method is implemented for

(how Add method is implemented for List in c#)

listobject.Add();
where List<User> listobject= new List<User>() is the declaration for the object.

I know that using List we can perform many operations on a fly and that too with type safety, but what I wonder is how id add method implemented so that it takes care of all that at run time.

Hope it doesnot copy the object and make adjustment on each add but I will keep my fingers crossed and wait for your reply 🙂

Answer 1

Using Reflector you can see exactly how its implemented.

public void Add(T item)
{
    if (this._size == this._items.Length)
    {
        this.EnsureCapacity(this._size + 1);
    }
    this._items[this._size++] = item;
    this._version++;
}

Following ‘EnsureCapacity’ …

private void EnsureCapacity(int min)
{
    if (this._items.Length < min)
    {
        int num = (this._items.Length == 0) ? 4 : (this._items.Length * 2);
        if (num < min)
        {
            num = min;
        }
        this.Capacity = num;
    }
}

And finally the setter for ‘Capacity’

public int Capacity
{
    get
    {
        return this._items.Length;
    }
    set
    {
        if (value != this._items.Length)
        {
            if (value < this._size)
            {
                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.value, ExceptionResource.ArgumentOutOfRange_SmallCapacity);
            }
            if (value > 0)
            {
                T[] destinationArray = new T[value];
                if (this._size > 0)
                {
                    Array.Copy(this._items, 0, destinationArray, 0, this._size);
                }
                this._items = destinationArray;
            }
            else
            {
                this._items = List<T>._emptyArray;
            }
        }
    }
}