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Null References, the Billion Dollar Mistake
jonr writes "'I call it my billion-dollar mistake. It was the invention of the null reference in 1965. At that time, I was designing the first comprehensive type system for references in an object oriented language (ALGOL W). My goal was to ensure that all use of references should be absolutely safe, with checking performed automatically by the compiler. But I couldn't resist the temptation to put in a null reference, simply because it was so easy to implement. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years. In recent years, a number of program analysers like PREfix and PREfast in Microsoft have been used to check references, and give warnings if there is a risk they may be non-null. More recent programming languages like Spec# have introduced declarations for non-null references. This is the solution, which I rejected in 1965.' This is an abstract from Tony Hoare Presentation on QCon. I'm raised on C-style programming languages, and have always used null pointers/references, but I am having trouble of grokking null-reference free language. Is there a good reading out there that explains this?"
It's hard to imagine life without the null pointer! That being said, the author is not really responsible for billions of dollars of mistakes, the programmers are.
If there is one thing I'll complain about, it's the choice of the value 0. It's almost impossible to trace it. When we do hardware debug of chips, we prefer to use a much more visible value such as 0xdeadbeef for instance. Otherwise a bad pointer will bland too much with all the uninitialized values out there.
In assembly, null has no particular meaning. If you dereference an address, you can do it in any range you like. It's just that 0 on most machines was not a good place to store anything, since it would typically be used to boot the OS or some other critical IO function that you don't want to mess up with. Thus null was born.
Fine. No null references. So I create the same thing by having a reference to some unique structure (probably named Null) and I still *fail to check for it*.
Null references don't kill programs. Programmers do.
-CZ
"Obviously the best way of accomplishing such a database is to denormalize any value that might be null"
That's normalizing -- the table in this example is de-normalized
Thanks,
--
Matt
Null-terminated strings. The bane of modern computing.
Yeah! Let's abolish them, life would be much simplerasdjkaRGfl$!jaekrbFt6634i2u23Q0CCA;DMF ASDJFERR
Summation 2
Zero. The bane of all. It was the gateway math to all modern problems. It would be so much simpler with just countables. Surely the current crisis, measured in trillions would look so much better without all those zeros.
Whoever it was who invented zero should take responsibility for all the worlds problems, ex nehilo.
-- Each tock of the Planck clock is a new world and here we are still life. --
Stroustrup's "C++ Programming Language" book introduces a concept called "resource acquisition is initialisation" that was eye-opening enough to me that it forever changed the way I think about code, and also seems relevant to your point.
The basic idea is that an object is always meant to represent something tangible. As an example, consider the design of file object that abstracts file I/O operations. As a developer, I've come across this one several times, it is normal that such objects have open and close methods, however that makes the design of the object in contradiction with Stroustrup's concept because open/close provided as methods rather than only called in the constructor/destructor means the object may be in existence yet be in a state where it is not associated with an open file. You basically have to grok that having a file object around that doesn't directly map to an open file just adds overhead to the system and is basically bad OO design in that in some sense that object is meaningless.
Apply the same concept to a reference and you have your answer. If a reference is pointing at nothing, then what is its purpose? The only thing a NULL reference is good for is when the software design ascribes a special meaning to the value NULL. Instead of just meaning address location 0, it gets subverted to mean "variable unassigned" or the "tail node of list" or somesuch. Ascribing multiple meanings to a variable value (especially pointers/references that are only ever meant to hold memory addresses) is one example of bad programming practice known as programming by side-effect which most people agree should be avoided.
Another point is that in most OO lanugages, references have an extra benefit of being more strongly typed than pointers, menaing that reference is guaranteed to only ever be pointing at an instantiated object of its specific type. That guarantee also gets broken when a reference can be NULL.
Just allocate the same amount of memory for everythi