Sep
12
I was discussing the little LINQ puzzle with Stephen Toub, and he brought up an idea which lead to another puzzle. I like this one even more than the previous one.
Why does the last line throw StackOverflowException?
IEnumerable<int> q = new int[] { 1, 2 }; q = from x in new int[] { 1, 2 } from y in q select x + y; q.ToArray();
And, how come the code sample runs just fine if you switch the order of the from clauses?
Tags: LINQ
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Do you have VB version?
Thanks
@Scorcels: Here is a VB version of the puzzle.
Dim q As IEnumerable(Of Integer) = Enumerable.Range(1, 2)
q = From x In Enumerable.Range(1, 2) _
From y In q _
Select x + y
q.ToArray()
haha, cmon people who uses VB anymore. Is it really that hard to figure out the difference between C# and VB?
Because there is recursive enumeration of q (-> closure) which is more evident if you rewrite it as:
q = new int[] { 1, 2 }.SelectMany(x => q, (x, y) => x + y);
when ToArray is called q is defined as above.
if you switch order there is no closure
q.SelectMany(y => new int[] { 1, 2 }, (x, y) => x + y);
[…] For a slightly harder challenge, check out the next puzzle. […]