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GOTOphobia considered harmful in C

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Re: GOTOphobia considered harmful in C

#231

Post by bdowling »

JohnBooty wrote: post #124
lolinder wrote: post #118

Earlier quoted context omitted.

CONTINUE and BREAK are quite different from GOTO in that they operate predictably given the current scope: their limitations make them incapable of creating the unstructured nightmare that Dijkstra was talking about. They're similar to a GOTO only in that they compile to a jump, but so do IF statements and FOR loops. Structured programming wasn't about eliminating jumps, it was about enforcing discipline in their use…

Not too many things make me shake my head harder than folks who consider continue/break to be GOTO equivalents. For the reasons you eloquently said. Additionally, far more often than not, continue/break allow you to avoid another form of complexity, bugs, and low comprehensibility: deeply nested conditionals.

CONTINUE and BREAK are simply jumps to the beginning of or just past the end of the current loop context. They are equivalent to GOTOs to particular program offsets without the programmer needing to create labels for those offsets. They do not have any magical meaning beyond that. You could even call them syntactic sugar.

Re: GOTOphobia considered harmful in C

#232

Post by l33t233372 »

kazinator wrote: post #166
preseinger wrote: post #106

Earlier quoted context omitted.

> Tail recursion is clearer and easier to reason about than loops tail recursion is a complex and subtle expression of control flow that requires substantial background knowledge to be able to even understand, much less reason about based on code on a page for loops are immediately intuitive to anyone, even without any programming training no idea how you can come to this conclusion. just ain't so

> tail recursion is a complex and subtle expression of control flow That is simply nonsense; it's just function application, ideally without having to think about state (or as little state as possible). > for loops are immediately intuitive to anyone, for loops are immediately intuitive to anyone That's just hand-waving without some sort of psychological data. Even if it were true, it would not be relevant because yo…

> the idea that for loops are somehow easier than recursion is definitely not from mainstream CS

I have never in my life heard a programmer say they think recursion is easier than loops.

Re: GOTOphobia considered harmful in C

#233

Post by Gibbon1 »

Swenrekcah wrote: post #15
jitl wrote: post #9

There have been a bunch of major security vulnerabilities due to mistakes involving GOTO in C, being used as suggested by the article. Here’s a memorable one: https://www.imperialviolet.org/2014/02/22/applebug.html

I’d say this was more due to the case not being properly enclosed in brackets. Many people seem to really dislike using the brackets but this is what that gets you.

More do to the case that they obviously didn't have unit tests for that piece of code.

Which is most frightening to me.

Re: GOTOphobia considered harmful in C

#234

Post by josefx »

bdowling wrote: post #229
lolinder wrote: post #118

Earlier quoted context omitted.

CONTINUE and BREAK are quite different from GOTO in that they operate predictably given the current scope: their limitations make them incapable of creating the unstructured nightmare that Dijkstra was talking about. They're similar to a GOTO only in that they compile to a jump, but so do IF statements and FOR loops. Structured programming wasn't about eliminating jumps, it was about enforcing discipline in their use…

> CONTINUE and BREAK are quite different from GOTO in that they operate predictably given the current scope CONTINUE, BREAK, and GOTO all operate predictably because they are deterministic operations. Each continues program execution at the directed explicit (goto) or implicit (continue or break) offset. There is no non-deterministic or unpredictable behavior whatsoever.

> operate predictably because they are deterministic operations

If I sat you in front of a computer generating numbers using a pseudo random number generator and gave you as context the last number it generated, could you make any prediction about the next number it generates?

Now if it used a prng that was known and standardized to only compute one number could you predict anything about the next number now?

Re: GOTOphobia considered harmful in C

#235

Post by staunton »

bdowling wrote: post #231
JohnBooty wrote: post #124

Earlier quoted context omitted.

Not too many things make me shake my head harder than folks who consider continue/break to be GOTO equivalents. For the reasons you eloquently said. Additionally, far more often than not, continue/break allow you to avoid another form of complexity, bugs, and low comprehensibility: deeply nested conditionals.

CONTINUE and BREAK are simply jumps to the beginning of or just past the end of the current loop context. They are equivalent to GOTOs to particular program offsets without the programmer needing to create labels for those offsets. They do not have any magical meaning beyond that. You could even call them syntactic sugar.

Yes, it's all compiled to jumps... The point of the discussion is that things like continue and break are easier to read and reason about because they can't just jump anywhere.

Re: GOTOphobia considered harmful in C

#236

Post by Natsu »

arp242 wrote: post #77
ufo wrote: post #50

I always encourage people to go read Dijkstra's GOTO paper, instead of just its title. It's a short and easy read, almost like a blog post. If you pay attention, you can see that the he was talking about spaghetti code vs structured code. It's better when the lexical structure of the source code maps to the execution structure. That is, if you know what is the current line being executed, you have a good idea of what…

The thing is that many people today have never encountered the sort of spaghetti code that Dijkstra was talking about in 1968. There's plenty of confusing and messy code around, but true spaghetti code that GOTOs all over the place and is nigh-impossible to follow has been extremely rare for a long time. I can't recall encountering it in the last 30 years. It easy to misunderstand what he was even talking about becau…

> I'm not that old, but I was unlucky enough to have programmed in an unstructured language where GOTO was the only way to use faux-subroutines in my teens.

Was that a Casio calculator? Because it was like that for me, only GOTOs existed. Learning about C and seeing these things called loops was a revelation because I had reinvented them with GOTOs already in my programming.

Re: GOTOphobia considered harmful in C

#237

Post by jjav »

snovv_crash wrote: post #125
jjav wrote: post #97

Earlier quoted context omitted.

> The thing is that many people today have never encountered the sort of spaghetti code that Dijkstra was talking about in 1968. Can't highlight this enough. The type of spaghetti code "goto considered harmful" was reacting to is basically impossible to create anymore, so anyone who didn't work on that type of code in the 80s or earlier probably hasn't seen it. And thus, is applying the mantra "goto considered harmfu…

Sure it's possible to have horrible spaghetti today. Just look at any pubsub architecture based system and tell me what piece of code executes after another. It's super popular, and it's GOTOs all over again, just with data instead.

This is a good observation, thanks. Yes, some of these cloud-native patterns do become what is essentially a spaghetti flow pattern, even if not in the fragmented pieces of code directly.

Re: GOTOphobia considered harmful in C

#238

Post by jjav »

josephg wrote: post #217
jjav wrote: post #97

Earlier quoted context omitted.

> The thing is that many people today have never encountered the sort of spaghetti code that Dijkstra was talking about in 1968. Can't highlight this enough. The type of spaghetti code "goto considered harmful" was reacting to is basically impossible to create anymore, so anyone who didn't work on that type of code in the 80s or earlier probably hasn't seen it. And thus, is applying the mantra "goto considered harmfu…

> The type of spaghetti code "goto considered harmful" was reacting to is basically impossible to create anymore, so anyone who didn't work on that type of code in the 80s or earlier probably hasn't seen it. Its still quite possible in assembly, where goto (JMP) is your only way to do control flow. But I doubt there's many people left who write and maintain large assembly programs. I imagine most programmers reach fo…

> Its still quite possible in assembly, where goto (JMP) is your only way to do control flow.

Yes, certainly very possible in assembly as it ever was. But as you note, few people are doing large scale assembly programs anymore. And I'd say that those who still do, are sufficiently experienced to avoid unstructured jump explosion in their code, hopefully.

Re: GOTOphobia considered harmful in C

#239

Post by bazoom42 »

jjav wrote: post #97
arp242 wrote: post #77

Earlier quoted context omitted.

The thing is that many people today have never encountered the sort of spaghetti code that Dijkstra was talking about in 1968. There's plenty of confusing and messy code around, but true spaghetti code that GOTOs all over the place and is nigh-impossible to follow has been extremely rare for a long time. I can't recall encountering it in the last 30 years. It easy to misunderstand what he was even talking about becau…

> The thing is that many people today have never encountered the sort of spaghetti code that Dijkstra was talking about in 1968. Can't highlight this enough. The type of spaghetti code "goto considered harmful" was reacting to is basically impossible to create anymore, so anyone who didn't work on that type of code in the 80s or earlier probably hasn't seen it. And thus, is applying the mantra "goto considered harmfu…

> Such as trying to avoid it in C for clean error handling, when there's no reason to avoid that.

Dijkstra would clearly disaprove of this use of goto. But he would blame the C language for making it necessary. Languages with structured cleanup (like the using clause in C#) does not need to use gotos for resource cleanup.

Dijkstras argument does not distinguish between short and long gotos or long or short functions. His argument applies to any use of goto.

Re: GOTOphobia considered harmful in C

#240

Post by zozbot234 »

jjav wrote: post #237
snovv_crash wrote: post #125

Earlier quoted context omitted.

Sure it's possible to have horrible spaghetti today. Just look at any pubsub architecture based system and tell me what piece of code executes after another. It's super popular, and it's GOTOs all over again, just with data instead.

This is a good observation, thanks. Yes, some of these cloud-native patterns do become what is essentially a spaghetti flow pattern, even if not in the fragmented pieces of code directly.

Async-await in general has all the same pitfalls. In fact, async programming, being based on reifying program continuations, is a GOTO equivalent in a quite literal sense.
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