Question

For the reasons that I still do not understand (see this SO question) multidimensional arrays in CLR do not implement IEnumerable<T>. So the following does not compile:

var m = new int[2,2] {{1, 2}, {3, 4}}; var q = from e in m select e; 

Then how come that this works just fine in VB.NET?

Sub Main()     Dim m(,) As Integer = {{1, 2}, {3, 4}}     Dim q = From e In m Select e      For Each i In q         Console.WriteLine(i)     Next End Sub 

Update:

The following code works because the C# compiler replaces the foreach with for loops to go through each dimension.

foreach(var e in m)     Console.WriteLine(e); 

becomes

int[,] numArray3 = new int[,] { { 2, 2 }, { 3, 3 } }; int upperBound = numArray3.GetUpperBound(0); int num4 = numArray3.GetUpperBound(1); for (int i = numArray3.GetLowerBound(0); i <= upperBound; i++) {     for (int j = numArray3.GetLowerBound(1); j <= num4; j++)     {         int num = numArray3[i, j];         Console.WriteLine(num);     } } 

Answer 1

The query works in VB.Net because it gets transformed into

IEnumerable<object> q = m.Cast<object>().Select<object, object>(o => o); 

This works because you can call Cast<TResult>() on IEnumerable, which [*,*] implements.

The LINQ query doesn’t work in C# because of the different approach the C# and VB.Net designers took. VB.Net takes a more hand holding approach and fixes your mistake and converts IEnumerable to IEnumerable<object> so it can be used.

In C#, you can simulate this by using

var q = from e in m.Cast<object>() select e;