.NET's Sometimes Nonsensical Logic
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There are certainly some odd decisions in the .NET class libraries. But I don't agree with you on this one. From a purely logical perspective, checking whether all members of an empty set satisfy a particular condition should always return
true- there are no members which don't satisfy the condition, so returningfalsewould be senseless. If you want an example of a nonsensical decision, look no further than theSystem.Text.Json.JsonElement'sTryGet...methods, which will throw an exception if the "JSON type" of the element is wrong. SoTryGetInt64will returntruefor{ "id": 42 }; returnfalsefor{ "id": 3.1415 }; and throw an exception for{ "id": "42" }. :wtf: Given the usualTryParsepattern, you might expect these methods to returnfalsefor any invalid input. But that's not what they do. They returnfalsefor some kinds of invalid input, and throw an exception for other kinds of invalid input.
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
So if you asked your sergeant if your platoon was all present and correct when in fact they'd all been blown to smithereens and the platoon was now devoid of soldiers, you would still expect the answer "Yes"?
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.NET's behavior is similar to the Principle of explosion It is not a fallacy, it is a matter of "careful what you wish, you just might get it". If you ask for multiple elements to satisfy a condition, you should be aware that you are, in fact, asking 2 questions: 1. I want at least 1 element 2. Each one of them satisfies the criterion. Do not count on the tooth fairy to satisfy your hidden criterion #1, make it explicit instead.
I agree - code defensively. Check that the collection has something to interrogate, and if it has, proceed to do so. Otherwise define the behaviour you want if it is empty. Don't be lazy!
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Someone really should start a weekly blog of inane .NET logic when it comes to what it does or does not throw an exception for vs. just behaving according to some default arbitrary choice. Entry #1: On an empty collection, `.Any()`, with our without a condition, always returns `false`, as any sane person would expect. However, `.All(condition)`, on an empty collection, returns `true`. HUH? If I look at an empty room and ask "Are all the people in there aliens?" the answer I expect is apparently YES? If ever there were a situation where a method call is so nonsensical that there is no possible objectively right way to handle that which everyone would agree on (thus justifying an Exception), it's asking about `All` the items in an empty collection. It's tantamount to division by zero. And yet on a `null` collection, even though these are all extension methods and perfectly capable of treating `null` as empty, it throws .NET's all time favorite and #1 most useless exception, `NulLReferenceException`. Clearly the .NET developers' goal is to ruin as many of my days as possible.
Wikipedias page on Empty set[^] shows the properties of an empty set - which defined this behavior. Personally I would have been very surprised if All() on an empty set would ever return false - as I one or another time managed to get "everything applies to all elements in the empty set" stuck in my head. :D
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No. :) Maybe its a mathematical mindset. "Is this condition true for every member of this (empty) set?" has to return
true, since there are no members of the set where the condition is not true. Similarly, "Is this condition true for any member of this (empty) set?" has to returnfalse, since there are no members of the set where the condition is true.
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
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I agree - code defensively. Check that the collection has something to interrogate, and if it has, proceed to do so. Otherwise define the behaviour you want if it is empty. Don't be lazy!
Oh after this episode I no longer use `All`; instead: public static bool AnyAndAll(this IEnumerable source, Func predicate) { if (source == null) return false; bool any = false; foreach (var item in source) { if (!predicate(item)) return false; any = true; } return any; }
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Someone really should start a weekly blog of inane .NET logic when it comes to what it does or does not throw an exception for vs. just behaving according to some default arbitrary choice. Entry #1: On an empty collection, `.Any()`, with our without a condition, always returns `false`, as any sane person would expect. However, `.All(condition)`, on an empty collection, returns `true`. HUH? If I look at an empty room and ask "Are all the people in there aliens?" the answer I expect is apparently YES? If ever there were a situation where a method call is so nonsensical that there is no possible objectively right way to handle that which everyone would agree on (thus justifying an Exception), it's asking about `All` the items in an empty collection. It's tantamount to division by zero. And yet on a `null` collection, even though these are all extension methods and perfectly capable of treating `null` as empty, it throws .NET's all time favorite and #1 most useless exception, `NulLReferenceException`. Clearly the .NET developers' goal is to ruin as many of my days as possible.
This may be considered a "dumb" response, but why not check for null and if not null, get a count, on your collection before attempting an action that presumes items in the collection?
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Someone really should start a weekly blog of inane .NET logic when it comes to what it does or does not throw an exception for vs. just behaving according to some default arbitrary choice. Entry #1: On an empty collection, `.Any()`, with our without a condition, always returns `false`, as any sane person would expect. However, `.All(condition)`, on an empty collection, returns `true`. HUH? If I look at an empty room and ask "Are all the people in there aliens?" the answer I expect is apparently YES? If ever there were a situation where a method call is so nonsensical that there is no possible objectively right way to handle that which everyone would agree on (thus justifying an Exception), it's asking about `All` the items in an empty collection. It's tantamount to division by zero. And yet on a `null` collection, even though these are all extension methods and perfectly capable of treating `null` as empty, it throws .NET's all time favorite and #1 most useless exception, `NulLReferenceException`. Clearly the .NET developers' goal is to ruin as many of my days as possible.
I figured I might be in the minority here, but suprised how overwhelmingly folks agree with Microsoft on `[Empty].All() == true`. Mathematically I totally get it. None of the items is false. Fine. But consider a real-world application and what I, as someone giving orders, would expect: Darth Vader is commanding the Imperial fleet and approaching a suspected Rebel base but is uncharacteristically concerned about civilian casualties for once. "Are there any civilian inhabitants of this planet, commander?" "No, Lord Vader," the commander replies. "Good, so they're all rebels?" "Yes, milord." "Sterilize the planet," Vader commands. The fleet spends the next four hours bombarding the planet, burning the entire surface and boiling the oceans, while Vader waits impatiently as he is eager to proceed to the next suspected target. Finally when the carnage is over, Vader asks, "Well done, Commander. How many Rebels did we kill?" "Well, um, none, milord," the commander meekly replies. "What do you mean?" "The planet was uninhabited." Vader initiates a force choke. "You said there were Rebels here!" The commander struggles to spit out his last words. "I said the inhabitants were all Rebels, not that there were any inhabitants."
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Someone really should start a weekly blog of inane .NET logic when it comes to what it does or does not throw an exception for vs. just behaving according to some default arbitrary choice. Entry #1: On an empty collection, `.Any()`, with our without a condition, always returns `false`, as any sane person would expect. However, `.All(condition)`, on an empty collection, returns `true`. HUH? If I look at an empty room and ask "Are all the people in there aliens?" the answer I expect is apparently YES? If ever there were a situation where a method call is so nonsensical that there is no possible objectively right way to handle that which everyone would agree on (thus justifying an Exception), it's asking about `All` the items in an empty collection. It's tantamount to division by zero. And yet on a `null` collection, even though these are all extension methods and perfectly capable of treating `null` as empty, it throws .NET's all time favorite and #1 most useless exception, `NulLReferenceException`. Clearly the .NET developers' goal is to ruin as many of my days as possible.
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The trouble is that you're explaining the logic of the implementation, whereas the question concerns the logic of the outcome. The outcomes of .Any() and .All() on empty collections are logically inconsistent. Logically the answer to whether anything in an empty collection or everything in the same collection meet some criterion is "No" in both cases. Similarly a null exception is absurd. My guess is that whoever coded and reviewed one of the two methods didn't first grasp the behaviour of the other. It happens a lot, in my experience.
Exactly. A lack of communication. The specs for the methods should have specified what the result should be for an empty set -- probably false.
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Microsoft is following the definition of Universal Quantification as applied to the empty set. See Universal quantification - Wikipedia[^]
That was an interesting read, as was this: [Vacuous truth - Wikipedia](https://en.wikipedia.org/wiki/Vacuous\_truth#:~:text=In mathematics and logic%2C a,does not really say anything.) I don't pretend to be a mathematician, but if all conditions can be satisfied by all members of an empty set, then all members of the empty set would satisfy the condition that their parent set is non-empty. If we took the other approach and said that no condition can be satisfied by all members of an empty set, then all members of the empty set would fail to satisfy the condition that their parent set is empty. Both approaches lead to contradictions, which is why the answer seems like it should be undefined.
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Someone really should start a weekly blog of inane .NET logic when it comes to what it does or does not throw an exception for vs. just behaving according to some default arbitrary choice. Entry #1: On an empty collection, `.Any()`, with our without a condition, always returns `false`, as any sane person would expect. However, `.All(condition)`, on an empty collection, returns `true`. HUH? If I look at an empty room and ask "Are all the people in there aliens?" the answer I expect is apparently YES? If ever there were a situation where a method call is so nonsensical that there is no possible objectively right way to handle that which everyone would agree on (thus justifying an Exception), it's asking about `All` the items in an empty collection. It's tantamount to division by zero. And yet on a `null` collection, even though these are all extension methods and perfectly capable of treating `null` as empty, it throws .NET's all time favorite and #1 most useless exception, `NulLReferenceException`. Clearly the .NET developers' goal is to ruin as many of my days as possible.
This actually makes perfect sense if you know set theory. It’s called vacuous truth Vacuous truth - Wikipedia[^]
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Someone really should start a weekly blog of inane .NET logic when it comes to what it does or does not throw an exception for vs. just behaving according to some default arbitrary choice. Entry #1: On an empty collection, `.Any()`, with our without a condition, always returns `false`, as any sane person would expect. However, `.All(condition)`, on an empty collection, returns `true`. HUH? If I look at an empty room and ask "Are all the people in there aliens?" the answer I expect is apparently YES? If ever there were a situation where a method call is so nonsensical that there is no possible objectively right way to handle that which everyone would agree on (thus justifying an Exception), it's asking about `All` the items in an empty collection. It's tantamount to division by zero. And yet on a `null` collection, even though these are all extension methods and perfectly capable of treating `null` as empty, it throws .NET's all time favorite and #1 most useless exception, `NulLReferenceException`. Clearly the .NET developers' goal is to ruin as many of my days as possible.
I know I may be alone on this but .. I just do not like Linq. It biases for easy-to-write at the expense of easy-to-understand (to say nothing of perf implications of making non-inlineable callbacks for each item in the list). Semantic details (like your example) matter, and I've spent way more hours debugging unexpected nuances like this, than I've saved by not writing a foreach loop in a little helper method.
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So if you asked your sergeant if your platoon was all present and correct when in fact they'd all been blown to smithereens and the platoon was now devoid of soldiers, you would still expect the answer "Yes"?
In your example, the sergeant is probably asking about the set of soldiers assigned to the platoon (regardless of status). In which case, the set isn't empty, and the answer is "no". However, if the sergeant was asking if all soldiers in your platoon who were capable of showing up were there, then the answer is "yes". Note: technically, the set still isn't empty, as you are presumably in your own platoon. However, the logic would still apply if the question was asked about another platoon where no one was left alive - everyone who was capable of showing up would be there...
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I agree. I find the behavior of
All()on an empty collection strange. If I'm told "all the members of a list of integers are greater than zero" I would expectAny(p => p > 0)on that list to returntrue. But if the list is empty,Any(p => p > 0)returnsfalse. That seems wrong. /raviMy new year resolution: 2048 x 1536 Home | Articles | My .NET bits | Freeware ravib(at)ravib(dot)com
Good point. So, you're saying that if `list.All(>0)` then we should be able to assume that `list.Any(>0)` is also true? Makes sense. However, it also makes sense that if `list.All(>0)` then `list.Any(<=0)` should be false, which it is, and we should be able to expect that if not `list.Any(<=0)` then `list.All(>0)` would be true, which it is (but wouldn't be if we changed it to work in your example). The problem is that either way, when working with null sets, we end up with some relationship which isn't fully transitive. For example, in SQL `x = null` and `x <> null` are both false (regardless of whether x is null or not, the only way to test for null is explicitly: `x is null` or `x is not null` ).
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I brought it up a while back and there was some back and forth on it. Apparently, malloc( 0 ) not returning NULL is deliberate. Here is what GCC does with some short bit of code printf("Hello world!\n"); printf( "call malloc(0)\n" ); sz = (char*)malloc(ZERO); printf( "Errno %d\n", errno ); if( sz == NULL ) printf( "returned NULL allocated zero bytes\n"); else printf( "NULL not returned from malloc, allocated 8 bytes\n" ); Hello world! call malloc(0) Errno 0 NULL not returned from malloc, allocated 8 bytes Apparently this is allowed by GCC. The argument is that it was successful Haven't tried it in VS.
"A little time, a little trouble, your better day" Badfinger
jmaida wrote:
Apparently, malloc( 0 ) not returning NULL is deliberate.
Standard says either is allowed.
jmaida wrote:
allocated 8 bytes
Without the actual standard, which costs money, I suspect the following is authoratative enough. MEM04-C. Beware of zero-length allocations - SEI CERT C Coding Standard - Confluence[^] Keep in mind that without that reference I thought it might have been undefined. Which means it could throw a system exception too. So probably better the way it is.
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I know I may be alone on this but .. I just do not like Linq. It biases for easy-to-write at the expense of easy-to-understand (to say nothing of perf implications of making non-inlineable callbacks for each item in the list). Semantic details (like your example) matter, and I've spent way more hours debugging unexpected nuances like this, than I've saved by not writing a foreach loop in a little helper method.
ShawnVN wrote:
I just do not like Linq.
Yep. And even worse when it was forced down as a database layer. Now I have to do a database profile on every single usage just to make sure it actually does the expected SQL rather than deciding to do something non-sensical.
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jmaida wrote:
Apparently, malloc( 0 ) not returning NULL is deliberate.
Standard says either is allowed.
jmaida wrote:
allocated 8 bytes
Without the actual standard, which costs money, I suspect the following is authoratative enough. MEM04-C. Beware of zero-length allocations - SEI CERT C Coding Standard - Confluence[^] Keep in mind that without that reference I thought it might have been undefined. Which means it could throw a system exception too. So probably better the way it is.
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Someone really should start a weekly blog of inane .NET logic when it comes to what it does or does not throw an exception for vs. just behaving according to some default arbitrary choice. Entry #1: On an empty collection, `.Any()`, with our without a condition, always returns `false`, as any sane person would expect. However, `.All(condition)`, on an empty collection, returns `true`. HUH? If I look at an empty room and ask "Are all the people in there aliens?" the answer I expect is apparently YES? If ever there were a situation where a method call is so nonsensical that there is no possible objectively right way to handle that which everyone would agree on (thus justifying an Exception), it's asking about `All` the items in an empty collection. It's tantamount to division by zero. And yet on a `null` collection, even though these are all extension methods and perfectly capable of treating `null` as empty, it throws .NET's all time favorite and #1 most useless exception, `NulLReferenceException`. Clearly the .NET developers' goal is to ruin as many of my days as possible.
The
Allseems to work the same as any other language conjunctions. Search for "vacuous truth" to read about the underlying set theory origin of this definition in logic, which all (or at least all non-esoteric) programming languages define all. The same logic you can find at least in Python, JavaScript, C/C++, PHP, etc. But on the other hand, if C# makes the methodAlldoes not return true without error on empty set, it will make C# special and unique language, so there might be benefits. -
You're not wrong. But you're not right either. Maths vs. Words :-D
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Someone really should start a weekly blog of inane .NET logic when it comes to what it does or does not throw an exception for vs. just behaving according to some default arbitrary choice. Entry #1: On an empty collection, `.Any()`, with our without a condition, always returns `false`, as any sane person would expect. However, `.All(condition)`, on an empty collection, returns `true`. HUH? If I look at an empty room and ask "Are all the people in there aliens?" the answer I expect is apparently YES? If ever there were a situation where a method call is so nonsensical that there is no possible objectively right way to handle that which everyone would agree on (thus justifying an Exception), it's asking about `All` the items in an empty collection. It's tantamount to division by zero. And yet on a `null` collection, even though these are all extension methods and perfectly capable of treating `null` as empty, it throws .NET's all time favorite and #1 most useless exception, `NulLReferenceException`. Clearly the .NET developers' goal is to ruin as many of my days as possible.
Have you ever heard of first-order logic - the logic which has been used formally for about 200 years (and informally much longer; on the order of 2000 years) for all sound reasoning in mathematics? Where it is obviously correct that "there is no x where P(x) is false" is equivalent with "for all x, P(x) holds" - because otherwise, that calculus would explode in your face ... Have you ever heard about vacuous truth? If not, please take some time to learn about these things. That's neither a .Net nor a Microsoft thing - it's basic logic knowledge. H.M.
