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This should never happen

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Re: This should never happen

#121

Post by pron »

ctdonath wrote: post #76
dzdt wrote: post #24

"This should never happen" is a design pattern of defensive programming. This is the same pattern for assert. The usual use is to catch errors caused by misuse of a method. There is some invariant that the method assumes but is not enforced by the type signature of the interface. So if something goes wrong in outside code, or someone tries to use the method incorrectly, the invariant is not satisfied. When you catch…

It's a sub-pattern of "ain't got time for dat". Developer knows that condition should never happen, but is not inclined to prove it (as represented by coding type checking or other handling) yet realizes it shouldn't be ignored outright (if only to document the unproven condition in code, or to shut the compiler up about incompleteness warnings).

> is not inclined to prove it (as represented by coding type checking or other handling)

This is known as a reachability problem that in the general case cannot be proven. So, "not inclined" may actually mean "can't (in any reasonable amount of time)".

Re: This should never happen

#122

Post by brianwawok »

z3t4 wrote: post #106
FiatLuxDave wrote: post #94

My favorite example of a "this should never happen" error was when I got a call from a customer, who started the conversation by asking, "Who is Brian?". I was caught a bit off guard, but I assumed the customer must know someone at the company, since Brian was the name of the previous electrical engineer/firmware programmer. So, I told them that Brian didn't work here any more, but was there anything that I could hel…

It's a good idea to haw a check for memory corruptions at regular intervals to keep your sanity.

How do you do that? I get on bootup you could do a little diddy, but how would you know if random bits are getting flipped? Seems tricky for an embedded device...

Re: This should never happen

#125

Post by cname »

rcarmo wrote: post #86
paulkaplan wrote: post #35

Using github to search like this reminds me of how a CS professor of mine would show the "best commit messages of the year" (homework was submitted via git) by looking for various patterns like all caps, all symbols, etc. http://www.slideshare.net/bsotomay/uchicago-cmsc-23300-the-b...

I preserved for posterity a colleague's unique commit style: https://gist.github.com/rcarmo/c671555169abbae83a1a

In case anyone looks at that and thinks it's cute or clever or fun... it's not. People will end up hating you for doing that. Okay, maybe hate is too strong, but it will certainly engender some strong negative feelings in anyone who has to try to figure out what you did (and when and why you did it).

Re: This should never happen

#127

Post by davesque »

Not trolling here. I'm curious why this is getting so much attention. Isn't saying "this should never happen" just making an assertion about the behavior of your code? As far as the apparent inconsistencies in the code seen in the results go, is it really fair to judge a random piece of code from a random person (and completely out of context)? Don't we all have scratch/experimental/incomplete code hosted on our github accounts?

Re: This should never happen

#128

Post by agoetz »

brianwawok wrote: post #122
z3t4 wrote: post #106

Earlier quoted context omitted.

It's a good idea to haw a check for memory corruptions at regular intervals to keep your sanity.

How do you do that? I get on bootup you could do a little diddy, but how would you know if random bits are getting flipped? Seems tricky for an embedded device...

SW Solution:

1. Store embedded system state in data structure.

2. Calculate a checksum for that data structure.

3. Verify that checksum is correct.

HW Solution:

Lockstep Execution/ECC memory, etc.

Re: This should never happen

#130

Post by notacoward »

groundCode wrote: post #44
ZeroGravitas wrote: post #2

Apparently things-that-shouldn't-happen happen 10x more in C code than the next nearest language.

or C developers have considered things that should not happen more than the next nearest language.

Totally THIS. Many C coding standards require that every return value be checked, every "switch" statement have a default case, etc. Programmers comply, but sometimes the conditions they're checking truly are impossible, so you end up with messages like these. By contrast, coding standards for languages with exceptions typically do not require such constant checking in the code. An uncaught exception is the moral equivalent of "this should never happen" but doesn't show up in a search like this. Without even getting into the issue of whether C programmers are really more diligent than Java or Python programmers (for example) there's a measurement problem to contend with here.
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