Why doesn't Array class expose its indexer directly?

Question

something to mention for answering:

1. Don\'t worry about variance, while the item in question is Array rather than

Answer 1

I think one reason why Array doesn't implement that indexer directly is because all the specific array types (like char[]) derive from Array.

What this means is that code like this would be legal:

char[] array = new char[10];
array[0] = new object();

Code like this shouldn't be legal, because it's not type-safe. The following is legal and throws an exception:

char[] array = new char[10];
array.SetValue(new object(), 0);

But SetValue() is not normally used, so this is not a big problem.

Answer 2

C# Specs "12.1.1 The System.Array type" says, "Note that System.Array is not itself an array-type"

Because it is not an array type.

And note that "6.1.6 Implicit reference conversions" says, "From a single-dimensional array type S[] to System.Collections.Generic.IList and its base interfaces, provided that there is an implicit identity or reference conversion from S to T"

C# Specs: http://www.microsoft.com/en-us/download/details.aspx?id=7029

About why the indexer access is so much of a mystery, check this other SO post: implicit vs explicit interface implementation

hope it helps.

Answer 3

Short answer:

System.Array is a base class for N-D arrays (not only 1-D), that's why 1-D indexer (object this[i]{get;set;}) cannot be a base member.

Long answer:

If you let's say create 2-dimensional array and try to access it's IList indexer:

Array a;
a=Array.CreateInstance(typeof(char), 1,1);
(a as IList)[0]='a';

You will get not supported exception.

Good question would be:

Why System.Array implement IList and IEnumerable while most of its implementation will throw NotSupportedException for non 1-D array??

One more interesting thing to mention. Technically non of the arrays have class-indexer internally in classic meaning. Classic meaning of Indexer is a property "Item" + get(+set) method(s). If you go deep to reflection you will see that typeof(string[]) does not have indexer property and it only has 2 methods Get and Set - those method declared in string[] class (not in base class, unlike Array.SetValue, Array.GetValue) and they are used for compile-time indexing.