Another fun github hack: if you browse the repo for a particular file, the URL will be something like
github.com/user/repo/blob/master/foo/bar/baz.py
But this file can change, meaning this url might not have the same content a week or month down the road. This is particularly troublesome when you have lines selected. To fix this, press `y` and your url will get expanded to include the current commit hash:
Or Knuth's take on it: https://pic.plover.com/knuth-GOTO.pdf [pdf] Structured Programming with go to Statements. Which helps to clarify why go to statements are both useful and worth minimizing, from a person who makes extensive use of goto statements in a lot of their code.
Not all gotos are made equal. A hundred gotos jumping forward to the same cleanup/error tail is very readable and actually reduces complexity over alternatives - which it’s obviously why it’s used. In many languages this type of construct has the form of try/catch/finally but those are glorified forward gotos.
Seeing even one goto jumping backward would be much more surprising, and seeing what made gotos get their bad rep, overlapping goto regions, would be completely shocking in any quality code base.
Kernels written in C are often full of gotos. There's nothing wrong with gotos per se, it's only harmful if that's your (or one of your) primary means of control flow, e.g. because you don't have other good options. BASIC for example had that problem back in the day.
Yes, but that was pretty much it: GOTO, GOSUB, and NEXT. And GOSUB is pretty much useless for building control flow equivalent to while/try/catch/... and even just if/else, or only "if" with more than one statement. NEXT works for only special cases of "for". So, most of the time, GOTO it is...
Gotos can be used to effectively accomplish try/catch in C. As long as you stick to a safe goto idiom like this then they can be useful. In general, an inexperienced programmer taught that goto is okay is probably not going to stick to safe idioms and will instead create spaghetti code, hence why they are steered away.
I'd be more likely to use setjmp/longjmp to accomplish try/catch in C than goto. Goto is fine for error handling, but exceptions are a bit different, since they have the try/catch/finally structure. Personally I prefer to avoid exceptions, but if I were forced to implement them I'd not use goto!
If you think it was a "peeve" or that he considered go to statements universally bad, maybe you should actually read the letter he wrote (NB: The title was not his, but Wirth's) and the discussion around it.
That's the original date on the file, but the comment being discussed (and much of the code in that function, it seems) was from 17 years ago. See the git-blame:
See the text of the comment: "12/12/91". The `git blame` is likely due to not having imported the previous history as commits when the original import to the git repo happened. I worked at a company that moved from VSS to TFS for a ~10 year code base. It took months for the consultants to get the import to preserve the history. Too bad this didn't happen in this repo.
edit: Found this [0]
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it.
Let it rip!
It's a weird feeling where if you work on this code, it must be like living archaeology, digging up remains, but at the same time sculpting new remains for the next generation. The other profession that must be like this is Law. In some ways this file feels more permanent than the blockchain. Although someone might come refactor it to Rust one day! If you do keep the comments at least!
As someone who has done some OS development and sysadmin work, I can relate to that quote. The 1st edition of Unix is over 50 years old and some of the legacy cruft that has accumulated since is so sedimented I swear it's going to turn into oil any minute now.
A meta comment on the comments on this article: as one might expect post-"goto fail"[1] there are a lot of people saying "hey this should be refactored, no goto!" I thought that at first when looking at the code, given what I remember of the Apple SSL vulnerability, and how "goto" has a smell. But, as it turns out, there are sane reasons to use goto in systems programming, especially as a kind of cleanup / finally block. TIL.
In plain c, goto is about the only sane way to do error handling in an ergonomic and easily maintainable way. The only cost is the goto stigma (which is generally justified).
The use of goto out (or similar) is idiomatic in a lot of kernel code. Since C has no notion of defer (like Go) or a finally block (like languages with exceptions), you place the code you want to always execute at the end, and then goto out instead of returning earlier.
The other option, in functions like this, is to have duplicated "deferred" execution scattered throughout the function at each return point. This is a maintenance nightmare as it can be hard to discern which code is actually part of the "deferred" block (and needs to be copied) and which isn't, at least at a glance. So differences in two return points are clues that something may be wrong, but requires further investigation to determine if they should or should not be the same. As a function grows in size, this becomes increasingly problematic.
goto usage in systems programming is actually much more prevalent and less of an anti-pattern/smell than in other contexts. This is because you often need to ensure every resource acquired during the function is cleaned up along each branch that the function could exit through. Because in systems programming you'll often do an operation, check if it succeeded and exit if not. The goto resource cleanup pattern avoids you having to duplicate the clean-up-partially-acquired-resouces at every early-return statement.
Looking through that file, I didn't see a single goto (but I could have missed one) that didn't go to one of: unlock_out, out, or error. I don't think there would be any diminishment of runtime efficiency if you dropped the goto statements, and it may actually improve performance to drop them since they correspond to a jump that could be removed from each of their occurrences. Though it would also increase the code size (everything in that section of code has to be replicated), so that could be an issue. Tradeoffs, would have to be measured to know for sure.
However, they do improve the maintainability of the code. I find it interesting, looking at them and having done a quick reread of Knuth's take on goto statements (for another comment I made here) that these uses correspond to what other languages possess as syntactic elements in the structured programming vein, which is one of the things he discusses in favor of both structured programming and goto statements. In favor of structured programming, you get new syntactic elements that provide useful semantics that make the code clearer. Why are we doing this jump? Oh, it's a conditional (if/then/else) or a loop (for, while). But when you lack the syntax and semantics for that, the goto statement can fill in the gaps (when used carefully, deliberately).
Specifically, out mostly corresponds to defer (in Go) or finally in other languages. error is like try/catch/finally in Java and others. unlock_out would be like the with statements you get in some other languages.
EDIT: Reexamined this specific source file. Most of the out sections are 0-2 statements in addition to the return. So in the 0 case, there ought to be a performance improvement by just returning, though I imagine a compiler can optimize the goto's away. In the 1-2 statement range it'd be a tossup on whether the increase in function size would cost more (cache miss and similar) than the indirection itself costs. I only saw one (it's a large file, I didn't look too closely) that had a larger out section than 2 statements, and that one had enough that the indirection is probably worth the performance cost.
But, in all cases (except the 0-statement case) it still is better from a maintainability perspective, whether or not it helps performance. In the 0-statement case, I wonder if they're vestigial. If there were other statements included that were dropped for some reason. But I'm not going to dig further into this because now it's time for me to study.
There also isn't a comment on every line, no test coverage that I can see, many functions are longer than 20 lines, and many of these source files are way too big at thousands of lines.
Probably easier to throw the whole thing out and start again.
> Without a winking smiley or other blatant display of humor, it is utterly impossible to parody a Creationist in such a way that someone won't mistake for the genuine article.
(the original phrasing)
But it works for other things as well. When a position is known to be, or believed to be, accepted by a significant number of people, and someone expresses that position, without knowing them it's impossible to tell if it's sarcastic or sincere. Even if it's presented in a somewhat exaggerated form, there are people would still hold some of the views the GP expresses.
> there are people would still hold some of the views the GP expresses.
"People"? Try 100% of (good) CS professors. Research clearly dictates that gotos are harmful. Lack of comments is just as bad. As for the test coverage, that's just their loss. I'm sure this "linux" project would have much higher velocity (agile term, look it up) if they used test driven development.
https://github.com/torvalds/linux/blob/f4bc5bbb5fef3cf421ba3...