Ayende @ Rahien

Diego Mijelshon commented on C# Coding Challenge: What will this code do?

Sat, 22 May 2010 17:40:15 GMT

"It works as you expect it to, but it doesn't look like it will work." -> which is why it's important to write the tests first. If it passes, you don't need to code anything else.

fschwiet commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 18:43:11 GMT

well the loop input from inst in new[]{inst1, inst2, new object()} where instanceToKey.TryGetValue(inst, out value) select value is equivalent to: new[] {inst1, inst2, new object()}.Where(inst => instanceToKey.TryGetValue(inst, out value)).Select( inst => value) I assumed this was equivalent to new[] {inst1, inst2, new object()}.Where(inst => instanceToKey.TryGetValue(inst, out value)).ToArray().Select( inst => value) But its not. So I was all sorts of wrong.

meisinger commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 16:13:45 GMT

Thats funny... have what is called "reverse reverse gotchas" all over the place Code that looks like it shouldn't work and doesn't work (oh I love the double negative) I haven't checked but I am pretty sure that I can also produce just the simple "gotcha" Code that looks like it should work but doesn't work

configurator commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 12:04:22 GMT

Daniel: I don't see why it would. And it doesn't.

Daniel commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 11:19:29 GMT

To everyone who thinks the is working correctly: change the order in the array so that the 3rd instance is in the middle: new[]{inst1, new object(), inst2} Then try to explain out why changing the position of an element that seems to be ignored changes the output of the program.

Steve Py commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 11:02:24 GMT

"This is actually what I call a reverse gotcha. It works as you expect it to, but it doesn't look like it will work. " rofl... Intentionally making something more obscure than it needs to be? That whole debate over Raven DB licensing must have put you in that sort of mood. ;)

Andrey Titov commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 10:46:14 GMT

I forgot second overload: public static IEnumerable ( this IEnumerable map, Func resultSelector ) { return ApplyMap(source, key => key, map, (item, key/*=item*/, value) => resultSelector(item, value)); } >

Andrey Titov commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 10:44:26 GMT

I'd rewrite this in something like: foreach (var keyCost in new[] { inst1, inst2, new object() } .ApplyMap(instanceToKey, (inst, key) => key) .ApplyMap(keyToCost, (key, cost) => new { key, cost })) { Console.WriteLine("Key: {0}, Cost: {1}", keyCost.key, keyCost.cost); } public static IEnumerable ( this IEnumerable keySelector, IDictionary map, Func resultSelector ) { foreach (var item in source) { TKey key = keySelector(item); TValue value; if (map.TryGetValue(key, out value)) { yield return resultSelector(item, key, value); } } } TryGetValue() newer fit well in LINQ :-( >

Felipe Fujiy commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 10:33:36 GMT

GetHashCode for classes by default return a unique token by instannce

Omer Mor commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 10:29:11 GMT

Why doesn't it look like it will work? Looking at the code, it seemed just fine to me.

Stefan Wenig commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 10:00:06 GMT

Sweet! Code that relies on delayed execution, string interning and the semantics of mutating captured variables. That's much better than last time's prefix decrement operator! Next time, can we have some lock-free multi-threaded code along with the question "what will this code print on an Itanium system?" Please! ;-) (you might need to specify the chipset though, but then at least participants can't just run the code to solve the quiz!)

Ayende Rahien commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 09:29:23 GMT

This is actually what I call a reverse gotcha. It works as you expect it to, but it doesn't look like it will work.

rvin100 commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 09:24:17 GMT

I'm agree with Steve too. It's a strange way to process, but you just got : Key: One, Cost: 1 Key: Two, Cost: 2 The third instance is just ignored...

kukabuka commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 08:17:42 GMT

I was going to agree with dan, but if you run the code it is just Key: One, Cost: 1 Key: Two, Cost: 2 inst1.Equals(inst2) = false. .GetHashCode() will reveal different hashes too. I guess that makes the difference to the Dictionary type.

Glenn commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 08:07:41 GMT

+1 to Steve's comment. TryGetValue returns false for the 3rd object and it's never selected.

dan commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 07:28:47 GMT

haven't touched .net for a while, but inst1 and inst2 are both new object() - will they have identical hash codes for the dictionary? if so, the result will be: Key: two, Cost: 2 Key: two, Cost: 2 Key: two, Cost: 2

Ken Egozi commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 06:54:31 GMT

Am I missing something? it should be the trivial "one"/1 and "two"/2 pairs

Steve Py commented on C# Coding Challenge: What will this code do?

Fri, 21 May 2010 06:51:02 GMT

Well it's bloody convoluded, but I couldn't see anything wrong with it. The 3rd instance will be ignored because of the TryGetValue. Key: One, Cost: 1 Key: Two, Cost: 2 I thought you might have a gotcha in there so I also tried it in .Net 3.5 and 4.0 but got the same result... Is something missing?