C# Language Specification

The System.Array type

The type System.Array is the abstract base type of all array types. An implicit reference conversion (§6.1.6) exists from any array type to System.Array, and an explicit reference conversion (§6.2.4) exists from System.Array to any array type. Note that System.Array is not itself an array-type. Rather, it is a class-type from which all array-types are derived.

At run-time, a value of type System.Array can be null or a reference to an instance of any array type.

2. Arrays and the generic IList interface

A one-dimensional array T[] implements the interface System.Collections.Generic.IList (IList for short) and its base interfaces. Accordingly, there is an implicit conversion from T[] to IList and its base interfaces. In addition, if there is an implicit reference conversion from S to T then S[] implements IList and there is an implicit reference conversion from S[] to IList and its base interfaces (§6.1.6). If there is an explicit reference conversion from S to T then there is an explicit reference conversion from S[] to IList and its base interfaces (§6.2.4). For example:

using System.Collections.Generic;

class Test
{
static void Main() {
string[] sa = new string[5];
object[] oa1 = new object[5];
object[] oa2 = sa;

IList lst1 = sa; // Ok

IList lst2 = oa1; // Error, cast needed
IList