What's the magic of arrays in C#

Question

int[] a = new int[5];
string[] b = new string[1];

The types of both a and b inherit from the abstract System.Array, but there is no real classes in the built-in library(it seems that there are some runtime types, you can't find the type defination class of an int[]). Can you tell me what happens while compiling? And why did they(the c# team) make this design(I mean why it's not something like Array<T>,instead they are using an abstract class with compiler magics)?

Answer 1

I would recommend getting the ECMA 335 spec and looking for Arrays if you want to know the low level detail: http://www.ecma-international.org/publications/standards/Ecma-335.htm

Answer 2

[] is a syntax(syntatic sugar) for defining Arrays in c#. Maybe CreateInstance will be replaced at runtime

 Array a = Array.CreateInstance(typeof(int), 5); 

is same as

int[] a = new int[5];

Source for CreateInstance (taken from reflector)

public static unsafe Array CreateInstance(Type elementType, int length)
{
    if (elementType == null)
    {
        throw new ArgumentNullException("elementType");
    }
    RuntimeType underlyingSystemType = elementType.UnderlyingSystemType as RuntimeType;
    if (underlyingSystemType == null)
    {
        throw new ArgumentException(Environment.GetResourceString("Arg_MustBeType"), "elementType");
    }
    if (length < 0)
    {
        throw new ArgumentOutOfRangeException("length", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
    }
    return InternalCreate((void*) underlyingSystemType.TypeHandle.Value, 1, &length, null);
}