Why do so many "developers" not understand 'null'?
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In Norwegian, the name of numeric zero is 'null'. So Norwegian kids 'sort of' have an excuse for confusing the two. But they are quite different. Zero is a distinct, well defined numeric value that you may treat 100% like any other numeric value. 'null' is nothing, not a numeric value, but a void. Emptiness. An abyss. Not at a valid numeric value. Some programming languages use the term 'void'; it is really much more descriptive. I feel like digging up my old Robert Heinlein collection to re-read the short story—And He Built a Crooked House[^]. The story tells about a crazy architect (in California, obviously :-)) who designs a house which is a 3-dimensional projection of a 4-dimensional cube, a tesseract. The night before the house owners move in, there is an earthquake that makes the house fold up as a true tesseract, in 4 dimensions, not just as a 3-dim projection. I believe that Heinlein has taken liberties in his description of how a real tesseract would appear. But his description of the view out one window, of a total emptiness, not even black, gave me shivers when I first read it, many years ago. It is a beautiful literary description of the concept of a 'null'. I think that I didn't fully understand the concept of null, void, myself until I read the Heinlein story.
trønderen wrote:
'null' is nothing, not a numeric value, but a void
This is not strictly true. In any (programming) language null is a value representing an abstract concept, just like an integer is a value representing an instance of a specific class of numbers, which are themselves an abstract concept used to quantify the world. It is true 'null' is the concept of 'not having a valid value' (i.e. nothing) but it is represented in a program using a value in various different lexical forms; null/NULL/etc. The OP clearly raised a very a good question that could, perhaps, be more pointedly made with the more abstract question; Why do so many developers not understand abstraction?
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Do you ever really have 0 apples from a weird sort of ship of Theseus-like perspective? Some cultures lack that sort of integer concept from a similar view... all apples are not created equal. No point talking about N of them as the potential distance from reality only increases the further from 1 you get. Forget apples to oranges, they don't even do apples to apples. More recently, quantum physics is saying there is no "nothing" and that there is always "quantum foam" that has always been. Maybe the young ones are so much smarter they look dumb. Nahhh haha. But maybe sending null across a wire as a matter of course is a little bit dumb too.
jochance wrote:
Do you ever really have 0 apples from a weird sort of ship of Theseus-like perspective?Prehistoric man? Pretty sure they know the concept of "no apples".
jochance wrote:
More recently, quantum physics is saying there is no "nothing" and that there is always "quantum foam" that has always been.
Physical BS. Quantum physics a bunch nonsense. Your mom always been fat, because quantum mech says so.
Bastard Programmer from Hell :suss: "If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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jochance wrote:
Do you ever really have 0 apples from a weird sort of ship of Theseus-like perspective?Prehistoric man? Pretty sure they know the concept of "no apples".
jochance wrote:
More recently, quantum physics is saying there is no "nothing" and that there is always "quantum foam" that has always been.
Physical BS. Quantum physics a bunch nonsense. Your mom always been fat, because quantum mech says so.
Bastard Programmer from Hell :suss: "If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
I guess my point was more that while I get the usefulness of bad models, they're still maybe bad in some specifics of practice. Which is still fine and all. It's not a full and total indictment of concepts. Tons of that self-referential integrity stuff going on in math, yeah? But most probably do not look at 0/null the same way as they look at other deeper mathematical concepts. It just sits there all happy exactly 1 unit from both -1 and 1. The reality seems to be that you can really never have 0 if you go splitting hairs. That said, it maybe makes it an even more perfect "init" value. Null though? Null was maybe never destined to be anything but a logical error. :java: "But I really want to store that something is specifically not known/unknowable!" "What about all the other stuff you don't even know you don't know?" "Look, you could've brought this up before we were a decade into RDBMS development. We're keeping it." "But I didn't know." "Exactly! And now we can record it!"
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I guess my point was more that while I get the usefulness of bad models, they're still maybe bad in some specifics of practice. Which is still fine and all. It's not a full and total indictment of concepts. Tons of that self-referential integrity stuff going on in math, yeah? But most probably do not look at 0/null the same way as they look at other deeper mathematical concepts. It just sits there all happy exactly 1 unit from both -1 and 1. The reality seems to be that you can really never have 0 if you go splitting hairs. That said, it maybe makes it an even more perfect "init" value. Null though? Null was maybe never destined to be anything but a logical error. :java: "But I really want to store that something is specifically not known/unknowable!" "What about all the other stuff you don't even know you don't know?" "Look, you could've brought this up before we were a decade into RDBMS development. We're keeping it." "But I didn't know." "Exactly! And now we can record it!"
jochance wrote:
But most probably do not look at 0/null the same way as they look at other deeper mathematical concepts.
Like ALL programmers, I had to deal with floats nearing zero, which is not NULL.
jochance wrote:
Null though? Null was maybe never destined to be anything but a logical error. [Coffee]
Nope. Let me explain, little padawan; 0 is having no apples. null is having no concept of apples.
Bastard Programmer from Hell :suss: "If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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jochance wrote:
But most probably do not look at 0/null the same way as they look at other deeper mathematical concepts.
Like ALL programmers, I had to deal with floats nearing zero, which is not NULL.
jochance wrote:
Null though? Null was maybe never destined to be anything but a logical error. [Coffee]
Nope. Let me explain, little padawan; 0 is having no apples. null is having no concept of apples.
Bastard Programmer from Hell :suss: "If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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And here I might've supposed you'd want people talking less about things they have no concept of. What's really important is the ability to dictate to the apple that it is inferior, and they mostly left that out altogether. lol
jochance wrote:
What's really important is the ability to dictate to the apple that it is inferior, and they mostly left that out altogether.
That makes no sense at all. Pears are superior tough :thumbsup:
Bastard Programmer from Hell :suss: "If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
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What I actually said was
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In C zero and NULL are very much the same thing.
Not that zero and null are the same everywhere.
We're both right. You're referring to an implementation, I was referring to the concept, the abstraction if you like, where null represents "value unknown" (or "not yet defined").
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trønderen has also said it well. Even the C language has confusion on this topic. Yes, I too believe that they have distinct meanings. Remember my posing the question of why is this a valid statement in C zero = 0; value = malloc( zero ); value is not null nor zero. Why would I want to allocate zero memory? Here is what ChatAI says In the C programming language, calling malloc(0) is allowed and returns a pointer to a memory block of size 0. This is specified in the C standard, which states that malloc(0) is equivalent to malloc(1). The reason for this behavior is that malloc is intended to allocate memory dynamically, and a request for 0 bytes of memory is considered a valid request. Allocating a block of memory with a size of 0 can be useful in certain situations, such as when you want to create a zero-length array or when you want to allocate memory that you will later reallocate to a different size using realloc. However, it is important to note that malloc does not guarantee that it will return a pointer to a block of memory that is truly 0 bytes in size. The implementation of malloc may choose to return a block of memory that is larger than the requested size, in which case the additional memory will not be accessible to your program. Clear as mud.
"A little time, a little trouble, your better day" Badfinger
Forgive my ignorance, but what is the point or purpose of a zero length array? Or at the lower level, reserving zero memory space?
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Forgive my ignorance, but what is the point or purpose of a zero length array? Or at the lower level, reserving zero memory space?
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I have just gone through four QA questions, each of which is an error caused by a null reference. And yet none of the posters seems to have any idea a) how to diagnose and fix it, or b) even what the error means. Do those of you who still work in teams find this is a common problem with younger team members?
The best concept I found to explain Java/C# object references to newcomers is to use a “leash” as the metaphor. Just because you have a leash in your hand, does not mean there is a dog on the other end. The object variable/leash is in the null/no-dog state. Many Java programming errors occur when multiple leashes are attached to the same dog. (And each leash holder thinks they have a unique dog!) [This is why immutable objects are a good idea] A new leash is attached to your dog every time you call a method and “pass” your leash by value. The method can “pull” your dog around or stuff it with treats. How do you free the dog so it becomes a stray so that the dog catcher/garbage collector can pick it up? Assign the variable/leash to null, of course. You can also mix types in with cat leashes vs dog leashes. This can work into leashes as interface holders. This works with C pointers to some extent. You can build on the metaphor to include pointer arithmetic. This is partly a reply to BillWoodruff but I wanted the reply at top level as I always found this a great metaphor.
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i tried to explain that to C# students (back when i had a few) by saying that a "null reference" is a named/typed placeholder/slot for a pointer/reference to something which is not defined. you, the programmer, have the "freedom" to create the named/typed slot. and, that the common exception "null reference" was what happened after your running code made demanded/needed/required a defined pointer. you have a favorite metaphor, or explanation ... i am all ears ! of course, now, Visual Studio/C# compiler (and ReSharper) are going to ... suggest a check. and, now, C#/>NET has new Attributes for static Type analysis: [^].
«The mind is not a vessel to be filled but a fire to be kindled» Plutarch
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To declare that it is known, but has a zero length value. E.g. if my middle name is a zero length string, null, it is known that I have no middle name. If it is null, I may have a middle name not yet entered into the database.
exactly. 0 means zero in contrast to 1 .. NULL means void or does not exist. However, this subtlety gets blurred by the programming and programmers making use of it. In C, Null is meant to be void address. zero is number 0. But if I do a boolean test on either one, I get false. If you print them they are both zero. Hence the blurriness. They are equivalent at programming level yet we know they mean two different things. Maybe C++ handles it differently. Go figure
"A little time, a little trouble, your better day" Badfinger
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We're both right. You're referring to an implementation, I was referring to the concept, the abstraction if you like, where null represents "value unknown" (or "not yet defined").
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Zero and null are not remotely the same thing. Zero is a value like any other. Null is the absence of any value, "undefined" if you like.
In JavaScript, undefined and null are two distinct values. The former meaning not defined and the latter meaning no value. Different concepts completely.
Jeremy Falcon
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I have just gone through four QA questions, each of which is an error caused by a null reference. And yet none of the posters seems to have any idea a) how to diagnose and fix it, or b) even what the error means. Do those of you who still work in teams find this is a common problem with younger team members?
Besides my full time job as a developer I also teach Computer Science one night a week at a community college. My observation is that the focus for young developers/students is HOW to do things rather than WHY things need to be done. Having mentored many developers over the last 40+ years I always focus on the WHY, because once they understand the WHY the HOW not only becomes fairly obvious they find they often have multiple HOWs to choose from. This is not unique to Computer Science, my 3 daughters are all teachers, High School English, High School Biology, and Elementary school. There is hope, perhaps slight and teacher dependent. The Elementary school teacher pioneered Common Core math in her school district and discovered kids she had taught math to that way in 1st and 2nd grade had significantly better performance in 4th grade. Of course, not universally, but sufficient to clearly see a difference.