Why do C# multidimensional arrays not implement IEnumerable<T>?

Solution 1:

The CLR has two different kinds of arrays: vectors which are guaranteed to be one-dimensional with a lower bound of 0, and more general arrays which can have non-zero bounds and a rank other than 0.

From section 8.9.1 of the CLI spec:

Additionally, a created vector with element type T, implements the interface System.Collections.Generic.IList<U> (§8.7), where U := T.

I have to say it seems pretty weird to me. Given that it already implements IEnumerable I don't see why it shouldn't implement IEnumerable<T>. It wouldn't make as much sense to implement IList<T>, but the simple generic interface would be fine.

If you want this, you could either call Cast<T> (if you're using .NET 3.5) or write your own method to iterate through the array. To avoid casting you'd have to write your own method which found the lower/upper bounds of each dimension, and fetched things that way. Not terribly pleasant.

Solution 2:

There is a workaround: you can convert any multidimensional array to an IEnumerable

public static class ArrayExtensions
{
    public static IEnumerable<T> ToEnumerable<T>(this Array target)
    {
        foreach (var item in target)
            yield return (T)item;
    }
}

Solution 3:

Zero bound single dimensional arrays implements both IEnumerable and IEnumerable<T>, but multi-dimensional arrays, unfortunately, implements only IEnumerable. The "workaround" by @Jader Dias indeed converts a multidimensional array to IEnumerable<T> but with a huge cost: every element of an array will be boxed.

Here is a version that won't cause boxing for every element:

public static class ArrayExtensions
{
    public static IEnumerable<T> ToEnumerable<T>(this T[,] target)
    {
        foreach (var item in target)
            yield return item;
    }
}