8 ms·

Traps to Developers

256 points by qouteall 1y ago

andunie 1y ago
That's a nice compendium of tips and useful information. I wonder if anyone can learn from this. I feel like I only understood what I already knew, or at least was very close to knowing. That's the same thing that happens with teaching manuals about any topic: they're organized in a way that makes sense and it's easy for people who already know the topics, but often very bad at teaching the same topics to an audience that doesn't know anything.
- skydhash 1y ago
  > with teaching manuals about any topic: they're organized in a way that makes sense and it's easy for people who already know the topic I think that the reason for a manual existence. To have a written record so we don't have to trust our memory. This is what most unix manuals are. You already know what the software can do, you just need to remember the specificity on how to get something done. > often very bad at teaching the same topics to an audience that doesn't know anything. What you need then is a tutorial (beginner seeking to learn) or a guide (beginner/intermediate seeking to do). Manuals in this case only serve to have better questions (Now you know what you don't know).
  - ozim 1y ago
    Kind of what I noticed for myself. When I was a kid I was trying to learn Linux and commands and it was disappointing. Over the years of using it I don’t need to learn it but I do need to look stuff up.
ngruhn 1y ago
A recent trap for me: Regex semantics is subtly different across languages. E.g. a{,3} matches between 0 and 3 "a" characters in Python. In JavaScript it matches the literal string "a{,3}".
- skydhash 1y ago
  Regex is more a technique than an actual specification. It would be best to find the time to go and read an introductory book about Theory of Computation where they explain the underlying mechanism.
  - ryandv 1y ago
    [flagged]
    - skydhash 1y ago
      It's half a chapter in most books I know. Or a subset of this 1h MIT videos [0], but the instructor also explains Finite Automata which is the basic mechanism that does all the stuff. [0]: https://www.youtube.com/watch?v=9syvZr-9xwk https://www.youtube.com/watch?v=9syvZr-9xwk
    - jraph 1y ago
      I'll assume sarcasm (from your comment history) but for people actually believing this first degree: good luck debugging an incorrect regex if you haven't practiced regexes. Especially if it was generated by an llm.
- danhau 1y ago
  I always use regex101 to develop my regexes. It allows you to switch between different engines.
- PhilipRoman 1y ago
  Honorable mention to [a-z], gotta be my favorite trap
  - dataflow 1y ago
    What's the trap for this one? I can't think of any engine that parses this to mean anything other than the letters a through z.
QuadmasterXLII 1y ago
CSS and C++ both have the “pick a subset and enforce that, or suffer” nature. On my to-do list: make a github action that requires manual override to merge any pull request with a css attribute not already present
- dschuessler 1y ago
  I am unsure how this is supposed to work for CSS. To my knowledge, most CSS properties cannot be substituted for each other. If the subset to be enforced is "CSS properties already present", what is a developer supposed to do if their CSS property is not already present? Change the design?
  - QuadmasterXLII 1y ago
    Well, (like C++) new css attributes are constantly added. This means you constantly have to choose between the old way or the new way: either is fine, but “pick old or new at random on a per pull request basis” isn’t.
    - dschuessler 1y ago
      You seem to assume that old CSS properties can be substituted for new ones. But as I said, to my knowledge this isn’t possible in most cases. Can you give an example of two CSS properties where 'either is fine, but only one should be used'? Or do you mean something else altogether by 'CSS attributes'?
      - QuadmasterXLII 1y ago
        The specific case that inspired this comment was a random mix of margin and gap
skobes 1y ago
The first "trap" on the page says "min-width: auto makes min width determined by content", but this is false outside of flex/grid. From MDN: "For block boxes, inline boxes, inline blocks, and all table layout boxes auto resolves to 0." https://developer.mozilla.org/en-US/docs/Web/CSS/min-width https://developer.mozilla.org/en-US/docs/Web/CSS/min-width
- deleted 1y ago
  [deleted]
- diggan 1y ago
  I guess the first trap should really be: "You cannot read any CSS property in isolation, as just like what the name implies, defaults and what values end up doing cascades through all the rules your document ends up using"
- jfengel 1y ago
  CSS cascade for text properties more or less makes sense. I have been unable to comprehend CSS layout from any perspective: page designer, implementer, user, anything. It must have someone in mind but I have no idea who I that is.
  - chrisweekly 1y ago
    https://every-layout.dev https://every-layout.dev has by far the best explanations and coherent usage of CSS I've encountered since I started doing webdev for a living in 1998.
    - lemonberry 1y ago
      Every Layout changed how I look at and do CSS. Great resource with a good philosophy behind it: CubeCSS. It really made CSS fun for me again.
  - skobes 1y ago
    Layout is more bazaar than cathedral. It has had many ideas mixed in by different contributors over decades.
deleted 1y ago
[deleted]
FFFXXX 1y ago
The part about C# volatile accesses using release-acquire ordering seems to be wrong if I read the C# docs correctly. "There is no guarantee of a single total ordering of volatile writes as seen from all threads of execution" https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/volatile https://learn.microsoft.com/en-us/dotnet/csharp/language-ref...
- charleslmunger 1y ago
  >A volatile write operation prevents earlier memory operations on the thread from being reordered to occur after the volatile write. A volatile read operation prevents later memory operations on the thread from being reordered to occur before the volatile read Looks like release/acquire to me? A total ordering would be sequential consistency.
  - FFFXXX 1y ago
    I think you are quoting from https://learn.microsoft.com/en-us/dotnet/api/system.threading.volatile?view=net-9.0 https://learn.microsoft.com/en-us/dotnet/api/system.threadin... "In C#, using the volatile modifier on a field guarantees that every access to that field is a volatile memory operation" This makes it sound like you are right and the volatile keyword has the same behaviour as the Volatile class which explicitly says it has acquire-release ordering. But that seems to contradict "The volatile keyword doesn't provide atomicity for operations other than assignment, doesn't prevent race conditions, and doesn't provide ordering guarantees for other memory operations." from the volatile keyword documentation?
    - judofyr 1y ago
      Acquire-release ordering provides ordering guarantees for all memory operations. If an acquire observes a releases, the thread is also guaranteed to see all the previous writes done by the other thread - regardless of the atomicity of those writes. (There still can't be any other data races though.) This volatile keyword appears to only consider that specific memory location whereas the Volatile class seem to implement acquire-release.
Someone 1y ago
> Java, C# and JS use UTF-16-like encoding for in-memory string That’s incorrect for Java, possibly also for C# and JS. In any language where strings are opaque enough types [1], the in-memory representation is an implementation detail. Java has been such a language since release 9 (https://openjdk.org/jeps/254 https://openjdk.org/jeps/254) [1] The ‘enough’ is because some languages have fully opaque types, but specify efficiency of some operations and through it, effectively proscribe implementation details. Having a foreign function interface also often means implementation details cannot be changed because doing that would break backwards compatibility. > JS use floating point for all numbers. The max accurate integer is 2⁵³−1 That is incorrect. Much larger integers can be represented exactly, for example 2¹⁰⁰. What is true is that 2⁵³−1 is the largest integer n such that n-1, n, and n+1 can be represented exactly in an IEEE double. That, in turn, means n == n-1 and n == n+1 both will evaluate to false, as expected in ‘normal’ arithmetic.
- debugnik 1y ago
  > possibly also for C# and JS The representation for C# is very much fixed, as it allows, and very commonly uses, direct access into the string buffer as a ReadOnlySpan<char> or a raw char pointer, where char is the type of UTF-16 codepoints. JS could maybe get away with it.
  - hinkley 1y ago
    When you have code that works a lot with strings the cost overhead of building an app on iso-latin-1 but encoding as utf-16 can be substantial. I think Java moved away from this back around 8, or possibly 9.
- scarface_74 1y ago
  I started to say something about C# strings and then I remembered the clusterfuck when it came to Windows development and strings and depending on which API you call, a string is represented by one of a dozen different ways. https://stackoverflow.com/questions/689211/interop-sending-string-from-c-sharp-to-c https://stackoverflow.com/questions/689211/interop-sending-s...
- deleted 1y ago
bradfitz 1y ago
> Golang use UTF-8 for in-memory string. Nope. It’s just bytes with no encoding. https://go.dev/blog/strings https://go.dev/blog/strings
- ivanjermakov 1y ago
  There is no such thing as "just bytes" when it comes to Unicode. UTF-8 is a way to represent Unicode codepoints in binary. But I agree that author's statement is wrong. Go stings are equivalent to byte slices.
  - bradfitz 1y ago
    Go strings are just bytes. There is no Unicode or encodings.
- qouteall 1y ago
  Corrected.
jmull 1y ago
This looks like not so much traps, but a list of things the author has learned. Much of it would only apply in certain relatively narrow contexts, but the contexts aren't necessarily mentioned. Some of it appears to be just wrong. I guess I'm saying: I would not take this literally, but as something almost like a stream-of-consciousness.
semperMade 1y ago
[dead]
koromak 1y ago
Does anyone truly understand all the little edge cases with CSS? I've write tons and tons of CSS, have done for a decade. I don't sit and think about the exact interactions, I just know a couple things that might work if I'm getting something unexpected. I don't really see it possible to commit that to memory, unless I literally start working on an interpreter myself.
- yurishimo 1y ago
  I think there can be a different way to think about CSS that can help with that feeling of never understanding it all. Recently I’ve heard people influential in the CSS world describe it as a “suggestion” to the browser. The browser has its own styles, the user might have some custom stylesheet on top of the browser’s version, extensions, etc etc and at some point CSS is really more a long list of “suggestions” about how the site should look. If you embrace that idea to the fullest, you can create some interesting designs/patterns that can be more resilient. The “downside” is that this way of writing css will likely made the pixel perfect head of the marketing department hate you unless they also write code. I think it’s also okay to say that some ways of writing css just aren’t relevant anymore. A good parallel in mind is building construction and general carpentry. These days, a quick 2x4 stud wall or insulated concrete forms is fast, cheap, and standardized around the world. However, many craftspeople still exist that will create beautiful joinery for what is ultimately a simple thing, but we can appreciate that art standalone. With CSS, I don’t suspect we will ever need to go back to floats or crazy background images or whatever but it’s nice that those tools are still there for not only the sake of back compat, but also as a way to tinker and “craft” something bespoke for a special project or just because you like it. Education will eventually catch up and grid and flexbox will keep gaining popularity until we decide that it’s too complicated and come up with some new algorithm. That can all be true though and you can bring value as a developer without knowing every single aspect to the public API.
  - 1718627440 1y ago
    But you need to, you know, actually float something in a text. I think to do it with flexbox/grid you need JS that calculates heights and than manually splits the text into boxes with heights, so essentially you are doing rendering. Also is there another way to position boxes side-by-side in an inline context without float?
mdaniel 1y ago
> A method that returns Optional<T> may return null. projects that do this drive me bananas If I had the emotional energy, I'd open a JEP for a new @java.lang.NonNullReference and any type annotated with it would be a compiler error to assign null to it public interface Alpha {} @java.lang.NonNullReference public interface Beta {} Alpha a = null; // ok Beta b = null; // compiler error javac will tolerate this Beta b; if (Random.randBoolean()) { b = getBeta(); } else { b = newBeta(); } but I would need to squint at the language specification to see if dead code elimination is a nicety or a formality Beta b; if (true) { b = getBeta(); } else { b = null; // I believe this will be elided and thus technically legal }
- Spivak 1y ago
  I question the wisdom of even having Optional<T> in a language with nulls. It would raise some eyebrows if a function in Python returned an Optional type object rather than T | None. You have to do a check either way unless you're doing some cute monad-y stuff.
  - catlover76 1y ago
    I think I get what you mean, but it's confusing ofc, because Optional[T] is the older type annotation in Python for T | None But like, when it comes to unwrappable optional/result thingies, there are libs in Python to mimic that kind of behavior from Rust and functional languages.
  - singron 1y ago
    Maybe this is cute monady stuff, but there isn't an equivalent to Optional<Optional<T>> with only null/None. You usually don't directly write that, but you might incidentally instantiate that type when composing generic code, or a container/function won't allow nulls.
    - charcircuit 1y ago
      In what context would you not want to treat Optional.of(null) and null as the same? It shouldn't be a big deal.
upghost 1y ago
> Unset variables. If DIR is unset, rm -rf $DIR/ becomes rm -rf /. Using set -u can make bash error when encountering unset variable. sweet mercy :O Someone call the Inquisition
- AnimalMuppet 1y ago
  Instead, say rm -rf $DIR That is, skip the trailing slash. Then if $DIR is not set, it becomes an invalid command, because no file names were supplied.
  - Terr_ 1y ago
    Better to make the requirement explicit, instead of relying on the argument-parsing details of rm or some other command: # Default message $ rm -rf "${DIR:?}" bash: DIR: parameter null or not set # Custom message $ rm -rf "${DIR:?It is not set OMG}" bash: DIR: It is not set OMG
- mdaniel 1y ago
  This was a very famous Steam bug
OptionOfT 1y ago
> Some routers and firewall silently kill idle TCP connections without telling application. Some code (like HTTP client libraries, database clients) keep a pool of TCP connections for reuse, which can be silently invalidated. To solve it you can configure system TCP keepalive. For HTTP you can use Connection: keep-alive Keep-Alive: timeout=30, max=1000 header. Once a TCP connection has been established there is no state on routers in between the 2 ends of the connection. The issue here is firewalls / NAT entries timing out. And indeed, no RSTs are sent. We had the issue in K8s with the conntrack module set too low. Now, you can try to put in an HTTP Keep-Alive, but that will not help you. The HTTP Keep-Alive is merely for connection re-use at the HTTP level, i.e. it doesn't close the connection: https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Keep-Alive https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/... An HTTP Keep-Alive does not generate any packages, it merely postpones the close. A TCP Keep-Alive generates packages which resets the timers.
- qouteall 1y ago
  Thanks I will correct that
- thwarted 1y ago
  s/packages/packets/
- altfredd 1y ago
  Note that TCP Keep-Alive might not play well with mobile devices. Mobile operating systems can use application-level keep-alive packets, because those can be easily attributed to individual applications: an applications receives a TCP/UDP packet during low-power CPU sleep mode, asks system to wake up (by e.g. taking a wake-lock), and the system takes note who caused the wake-up. TCP Keep-Alive happens below application level, so it may be disabled, even when application can still be reached.
nayuki 1y ago
Largely a good listicle. Some feedback: > Unicode unification. Different characters in different language use the same code point. Different languages' font variants render the same code point differently. 語 This isn't a trap. The given example character means the same thing in Chinese and Japanese, and the Japanese version was imported from China. People from both languages recognize both font variants as the same conceptual character. The author is making it sound like the letter 'A' in English should have a different code point than an 'A' in French. Or that a lowercase 'a' with the top tail should be a different character than a lowercase 'a' without the top tail. Anyway, this is discussed at length in https://en.wikipedia.org/wiki/Han_unification https://en.wikipedia.org/wiki/Han_unification > There is a negative zero -0.0 which is different to normal zero. The negative zero equals zero when using floating point comparision. Normal zero is treated as "positive zero". And there are two ways to distinguish negative zero from normal zero: By their integer bit patterns, or by the fact that 1.0/-0.0 == -Inf vs. 1.0/0.0 == +Inf. > It's recommended to configure the server's time zone as UTC. Big yes. I use UTC for servers, logs, photos, and anything that is worth archiving and timestamping properly. Local time is only for colloquial use. > For integer (low + high) / 2 may overflow. A safer way is low + (high - low) / 2 Yes, but if low and high could be negative numbers, then you've just shifted the overflow to a different range. This matters for general binary search over an integer range, as opposed to unsigned binary search over an array. > C/C++ I'm going to throw in one of my lists of pitfalls - just using integer types and arithmetic correctly in C/C++ is a massive developer trap. That's like the most basic thing in programming. https://www.nayuki.io/page/summary-of-c-cpp-integer-rules https://www.nayuki.io/page/summary-of-c-cpp-integer-rules > Rebase can rewrite history "Can" is a weasel word; rebase does nothing but rewrite history.
- cyberax 1y ago
  > The author is making it sound like the letter 'A' in English should have a different code point than an 'A' in French. Or that a lowercase 'a' with the top tail should be a different character than a lowercase 'a' without the top tail. But we do have А and A. Even though they look the same. And unified Han characters are often quite distinct, it tripped me up as a learner of Chinese more than once. For example, a very common character '喝' (drink) looks quite a bit different: https://en.wiktionary.org/wiki/%E5%96%9D https://en.wiktionary.org/wiki/%E5%96%9D - they have a different number of strokes even. And I can't even copy-paste it here to demonstrate, because it changes form once I copy it from the Wikipedia article. Han unification is a mess.
gooodvibes 1y ago
> There are subtle differences between numpy and pytorch. This isn't really a trap, and it doesn't help anyone; it looks like "I got burned but I don't want to share the specifics".
busymom0 1y ago
> Division is much slower than multiplication (unless using approximation). Dividing many numbers with one number can be optimized by firstly computing reciprocal then multiply by reciprocal. Is this a general fact or specific to a language?
- whobre 1y ago
  It's generally true even for CPU instructions: https://electronics.stackexchange.com/questions/280673/why-does-hardware-division-take-much-longer-than-multiplication https://electronics.stackexchange.com/questions/280673/why-d...
- ethan_smith 1y ago
  It's hardware-level - division requires more CPU cycles than multiplication on most processor architectures, making this optimization pattern relevant across virtually all programming languages.
joshdavham 1y ago
> Python: - Default argument is a stored value that will not be re-created on every call. PSA for anyone working with datetime variables!
- naet 1y ago
  I'm not regularly a python developer and I just spent a ton of time earlier this week tripped up by the default argument being a stored value. I was using to make an empty set if no set was passed in... but the set was not always empty because it was being reused. Took me forever to figure out what was going on.
jonathrg 1y ago
> If you already use locking, no volatile needed. Kinda misleading. volatile is for memory mapped I/O and such. volatile means the memory access really happens
- qouteall 1y ago
  I changed the wording of it.
ikonst 1y ago
yaml: https://www.bram.us/2022/01/11/yaml-the-norway-problem/ https://www.bram.us/2022/01/11/yaml-the-norway-problem/ bash: errexit depends on caller's context, will utterly fail you one day: https://lists.gnu.org/archive/html/bug-bash/2012-12/msg00093.html https://lists.gnu.org/archive/html/bug-bash/2012-12/msg00093...
- qouteall 1y ago
  Added
DatDay 1y ago
LF vs CRLF
- mdaniel 1y ago
  Which is incredibly painful on Windows systems doing a git clone of shell scripts, since core.autocrlf is often helpful, but not for shell scripts, since it causes the weirdest looking error messages: MSYS$ cat build.sh #!/bin/bash echo "hello, world" MSYS$ ./build.sh : not found: 2: build.sh e.g. https://askubuntu.com/questions/370124/not-found-error-when-running-a-script-with-sh https://askubuntu.com/questions/370124/not-found-error-when-... Polite projects will have .gitattributes specifying that .sh or .bash or bin/* or whatever are to always checkout with eol=lf <https://git-scm.com/docs/gitattributes#_eol https://git-scm.com/docs/gitattributes#_eol> As best I can tell, .ps1 does tolerate Unix lf but I'd bet good money that .bat and .cmd definitely do not
- qouteall 1y ago
  Thanks for reminding. Added.
aragilar 1y ago
"Associativity law and distribution law doesn't strictly hold because of inaccuracy." should be due to precision loss not inaccuracy (they are different).
- qouteall 1y ago
  updated
nextworddev 1y ago
The biggest trap of all: building things that no one, including yourself, wants
- geuis 1y ago
  I would agree on the self part. But otherwise this point of view is distinctly in contrast with the recently republished "work on things that don't scale" article from pg. Also as a corollary, I was thinking about games from the 90s I spent hundreds of hours playing back then earlier today. Bolo and Escape Velocity in particular come to mind. They were "simple" games with immense depth. But after some fruitless searching, all I find is scattered questions and comments over the last few years looking for modern equivalents are a handful of recommendations for games that are no longer developed or are defunct. There's clear prior evidence of both success and lack of modern supply. Want to have a minimally minor successful game with established nostalgic audience? Make a new version of EV that is that game at its core. Don't be fancy, just do the thing Ambrosia did. Expand from there. The simple model is look forward, and also look back. The first itch is small. For yourself. Find some others with a similar itch. The hard part is pushing your idea into something more people want. That's where pg's 2013 article comes in to play. That's the hard part. But that leaves a huge space between 0 and 10 where someone can find a successful niche. Hell I've thought about trying to make a modern EV. It's tantalizing. But I've never made a game in my life. Ok I've rewritten Game of Life a lot. Good concept to try new ideas with. But the amount of work for a solo dev trying to recapture that original magic with no background in game dev is daunting.
  - nextworddev 1y ago
    well if you at least build something you want, you are doing something that doesn't scale no?
chrismorgan 1y ago
Adjacent to the bit about 100vh, I’d add an item about the much older fundamental stupidity of viewport units, which Firefox tried to fix but no one else got on board and so they eventually removed their patch and went back to being as broken as everyone else. That is: they ignore scrollbars. Use a platform with 17px-wide scrollbars, and in a document with vertical scrolling, 100vw is now 100% of the viewport width… plus 17px. People get this wrong all the time, and it’s only increased as more platforms have switched to overlay scrollbars by default. > Blur does not consider ambient things. Need to make that backdrop blur. > Whitespace collapse. HTML Whitespace is Broken I always hated that article title. It’s not broken, it’s just different from what you occasionally expected, mostly for very good reasons that let it do what you expected most of the time. I also disagreed with some significant other parts of it: https://news.ycombinator.com/item?id=42971415 https://news.ycombinator.com/item?id=42971415. > Two concepts: code point (rune), grapheme cluster: I have problems with this lot. Firstly: add code units. When dealing with UTF-8 and you can access individual bytes, they’re UTF-8 code units. When dealing with UTF-16 and you can access 16-bit values, including surrogates, they’re UTF-16 code units. Secondly: don’t talk about code points in general, talk about scalar values, which are what code points would have been were it not for that accursèd abomination UTF-16. Specifically, scalar values excludes the surrogate code points. Sensible things work with scalar values. Python is the only thing I can think of that gets this wrong: its strings are sequences of code points, so you can represent lone surrogates (representable in neither UTF-8 nor UTF-16). This is so stupid. Thirdly: ditch the alias “rune”, Go invented it and it never caught on. I don’t know of anything else that uses the term (though maybe a few things do), and the term rune gets used for other unrelated things (e.g. in Svelte 5). > Some text files have byte order mark (BOM) at the beginning. For example, EF BB BF is a BOM that denotes the file is in UTF-8 encoding. It's mainly used in Windows. Some non-Windows software does not handle BOM. BOM was about endianness, and U+FEFF. Link to https://en.wikipedia.org/wiki/Byte_order_mark https://en.wikipedia.org/wiki/Byte_order_mark. It made sense in UTF-16 and UTF-32: for UTF-16, if the file starts with FE FF it’s UTF-16BE, if FF FE it’s UTF-16LE. UTF-8 application of it was always a mess, never really caught on, and I think can fairly be considered completely obsolete now: the typical person or software will never encounter it. Very little software will actually handle it any more. Fortunately, it doesn’t tend to matter much: U+FEFF is the BOM for a reason, it’s ZERO WIDTH NO-BREAK SPACE. > YAML: I’d add “disallows Tab indentation”. It’s the only thing I can immediately think of that’s like that. (Make is roughly the opposite, recipe lines having to start with a single Tab. Python doesn’t let you mix spaces and tabs. These are all I can immediately think of.)
decasia 1y ago
For what it's worth, I really enjoyed "Traceroute Isn't Real." I have noticed for quite a while that the data from it is at best patchy, often apparently meaningless. So it's helpful to see the explanation of why that is expected behavior: https://gekk.info/articles/traceroute.htm https://gekk.info/articles/traceroute.htm (If it's outdated I'm curious if anyone knows relevant updates?)

256 points by qouteall 1y ago

That's a nice compendium of tips and useful information. I wonder if anyone can learn from this. I feel like I only understood what I already knew, or at least was very close to knowing. That's the same thing that happens with teaching manuals about any topic: they're organized in a way that makes sense and it's easy for people who already know the topics, but often very bad at teaching the same topics to an audience that doesn't know anything.

skydhash 1y ago
> with teaching manuals about any topic: they're organized in a way that makes sense and it's easy for people who already know the topic I think that the reason for a manual existence. To have a written record so we don't have to trust our memory. This is what most unix manuals are. You already know what the software can do, you just need to remember the specificity on how to get something done. > often very bad at teaching the same topics to an audience that doesn't know anything. What you need then is a tutorial (beginner seeking to learn) or a guide (beginner/intermediate seeking to do). Manuals in this case only serve to have better questions (Now you know what you don't know).
- ozim 1y ago
  Kind of what I noticed for myself. When I was a kid I was trying to learn Linux and commands and it was disappointing. Over the years of using it I don’t need to learn it but I do need to look stuff up.

ngruhn 1y ago

A recent trap for me: Regex semantics is subtly different across languages. E.g. a{,3} matches between 0 and 3 "a" characters in Python. In JavaScript it matches the literal string "a{,3}".

skydhash 1y ago
Regex is more a technique than an actual specification. It would be best to find the time to go and read an introductory book about Theory of Computation where they explain the underlying mechanism.
- ryandv 1y ago
  [flagged]
  - skydhash 1y ago
    It's half a chapter in most books I know. Or a subset of this 1h MIT videos [0], but the instructor also explains Finite Automata which is the basic mechanism that does all the stuff. [0]: https://www.youtube.com/watch?v=9syvZr-9xwk https://www.youtube.com/watch?v=9syvZr-9xwk
  - jraph 1y ago
    I'll assume sarcasm (from your comment history) but for people actually believing this first degree: good luck debugging an incorrect regex if you haven't practiced regexes. Especially if it was generated by an llm.
danhau 1y ago
I always use regex101 to develop my regexes. It allows you to switch between different engines.
PhilipRoman 1y ago
Honorable mention to [a-z], gotta be my favorite trap
- dataflow 1y ago
  What's the trap for this one? I can't think of any engine that parses this to mean anything other than the letters a through z.

QuadmasterXLII 1y ago

CSS and C++ both have the “pick a subset and enforce that, or suffer” nature. On my to-do list: make a github action that requires manual override to merge any pull request with a css attribute not already present

dschuessler 1y ago
I am unsure how this is supposed to work for CSS. To my knowledge, most CSS properties cannot be substituted for each other. If the subset to be enforced is "CSS properties already present", what is a developer supposed to do if their CSS property is not already present? Change the design?
- QuadmasterXLII 1y ago
  Well, (like C++) new css attributes are constantly added. This means you constantly have to choose between the old way or the new way: either is fine, but “pick old or new at random on a per pull request basis” isn’t.
  - dschuessler 1y ago
    You seem to assume that old CSS properties can be substituted for new ones. But as I said, to my knowledge this isn’t possible in most cases. Can you give an example of two CSS properties where 'either is fine, but only one should be used'? Or do you mean something else altogether by 'CSS attributes'?
    - QuadmasterXLII 1y ago
      The specific case that inspired this comment was a random mix of margin and gap

skobes 1y ago

The first "trap" on the page says "min-width: auto makes min width determined by content", but this is false outside of flex/grid. From MDN: "For block boxes, inline boxes, inline blocks, and all table layout boxes auto resolves to 0." https://developer.mozilla.org/en-US/docs/Web/CSS/min-width https://developer.mozilla.org/en-US/docs/Web/CSS/min-width

deleted 1y ago
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diggan 1y ago
I guess the first trap should really be: "You cannot read any CSS property in isolation, as just like what the name implies, defaults and what values end up doing cascades through all the rules your document ends up using"
jfengel 1y ago
CSS cascade for text properties more or less makes sense. I have been unable to comprehend CSS layout from any perspective: page designer, implementer, user, anything. It must have someone in mind but I have no idea who I that is.
- chrisweekly 1y ago
  https://every-layout.dev https://every-layout.dev has by far the best explanations and coherent usage of CSS I've encountered since I started doing webdev for a living in 1998.
  - lemonberry 1y ago
    Every Layout changed how I look at and do CSS. Great resource with a good philosophy behind it: CubeCSS. It really made CSS fun for me again.
- skobes 1y ago
  Layout is more bazaar than cathedral. It has had many ideas mixed in by different contributors over decades.

deleted 1y ago

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FFFXXX 1y ago

The part about C# volatile accesses using release-acquire ordering seems to be wrong if I read the C# docs correctly. "There is no guarantee of a single total ordering of volatile writes as seen from all threads of execution" https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/volatile https://learn.microsoft.com/en-us/dotnet/csharp/language-ref...

charleslmunger 1y ago
>A volatile write operation prevents earlier memory operations on the thread from being reordered to occur after the volatile write. A volatile read operation prevents later memory operations on the thread from being reordered to occur before the volatile read Looks like release/acquire to me? A total ordering would be sequential consistency.
- FFFXXX 1y ago
  I think you are quoting from https://learn.microsoft.com/en-us/dotnet/api/system.threading.volatile?view=net-9.0 https://learn.microsoft.com/en-us/dotnet/api/system.threadin... "In C#, using the volatile modifier on a field guarantees that every access to that field is a volatile memory operation" This makes it sound like you are right and the volatile keyword has the same behaviour as the Volatile class which explicitly says it has acquire-release ordering. But that seems to contradict "The volatile keyword doesn't provide atomicity for operations other than assignment, doesn't prevent race conditions, and doesn't provide ordering guarantees for other memory operations." from the volatile keyword documentation?
  - judofyr 1y ago
    Acquire-release ordering provides ordering guarantees for all memory operations. If an acquire observes a releases, the thread is also guaranteed to see all the previous writes done by the other thread - regardless of the atomicity of those writes. (There still can't be any other data races though.) This volatile keyword appears to only consider that specific memory location whereas the Volatile class seem to implement acquire-release.

Someone 1y ago

> Java, C# and JS use UTF-16-like encoding for in-memory string That’s incorrect for Java, possibly also for C# and JS. In any language where strings are opaque enough types [1], the in-memory representation is an implementation detail. Java has been such a language since release 9 (https://openjdk.org/jeps/254 https://openjdk.org/jeps/254) [1] The ‘enough’ is because some languages have fully opaque types, but specify efficiency of some operations and through it, effectively proscribe implementation details. Having a foreign function interface also often means implementation details cannot be changed because doing that would break backwards compatibility. > JS use floating point for all numbers. The max accurate integer is 2⁵³−1 That is incorrect. Much larger integers can be represented exactly, for example 2¹⁰⁰. What is true is that 2⁵³−1 is the largest integer n such that n-1, n, and n+1 can be represented exactly in an IEEE double. That, in turn, means n == n-1 and n == n+1 both will evaluate to false, as expected in ‘normal’ arithmetic.

debugnik 1y ago
> possibly also for C# and JS The representation for C# is very much fixed, as it allows, and very commonly uses, direct access into the string buffer as a ReadOnlySpan<char> or a raw char pointer, where char is the type of UTF-16 codepoints. JS could maybe get away with it.
- hinkley 1y ago
  When you have code that works a lot with strings the cost overhead of building an app on iso-latin-1 but encoding as utf-16 can be substantial. I think Java moved away from this back around 8, or possibly 9.
scarface_74 1y ago
I started to say something about C# strings and then I remembered the clusterfuck when it came to Windows development and strings and depending on which API you call, a string is represented by one of a dozen different ways. https://stackoverflow.com/questions/689211/interop-sending-string-from-c-sharp-to-c https://stackoverflow.com/questions/689211/interop-sending-s...
deleted 1y ago

bradfitz 1y ago

> Golang use UTF-8 for in-memory string. Nope. It’s just bytes with no encoding. https://go.dev/blog/strings https://go.dev/blog/strings

ivanjermakov 1y ago
There is no such thing as "just bytes" when it comes to Unicode. UTF-8 is a way to represent Unicode codepoints in binary. But I agree that author's statement is wrong. Go stings are equivalent to byte slices.
- bradfitz 1y ago
  Go strings are just bytes. There is no Unicode or encodings.
qouteall 1y ago
Corrected.

jmull 1y ago

This looks like not so much traps, but a list of things the author has learned. Much of it would only apply in certain relatively narrow contexts, but the contexts aren't necessarily mentioned. Some of it appears to be just wrong. I guess I'm saying: I would not take this literally, but as something almost like a stream-of-consciousness.

semperMade 1y ago

[dead]

koromak 1y ago

Does anyone truly understand all the little edge cases with CSS? I've write tons and tons of CSS, have done for a decade. I don't sit and think about the exact interactions, I just know a couple things that might work if I'm getting something unexpected. I don't really see it possible to commit that to memory, unless I literally start working on an interpreter myself.

yurishimo 1y ago
I think there can be a different way to think about CSS that can help with that feeling of never understanding it all. Recently I’ve heard people influential in the CSS world describe it as a “suggestion” to the browser. The browser has its own styles, the user might have some custom stylesheet on top of the browser’s version, extensions, etc etc and at some point CSS is really more a long list of “suggestions” about how the site should look. If you embrace that idea to the fullest, you can create some interesting designs/patterns that can be more resilient. The “downside” is that this way of writing css will likely made the pixel perfect head of the marketing department hate you unless they also write code. I think it’s also okay to say that some ways of writing css just aren’t relevant anymore. A good parallel in mind is building construction and general carpentry. These days, a quick 2x4 stud wall or insulated concrete forms is fast, cheap, and standardized around the world. However, many craftspeople still exist that will create beautiful joinery for what is ultimately a simple thing, but we can appreciate that art standalone. With CSS, I don’t suspect we will ever need to go back to floats or crazy background images or whatever but it’s nice that those tools are still there for not only the sake of back compat, but also as a way to tinker and “craft” something bespoke for a special project or just because you like it. Education will eventually catch up and grid and flexbox will keep gaining popularity until we decide that it’s too complicated and come up with some new algorithm. That can all be true though and you can bring value as a developer without knowing every single aspect to the public API.
- 1718627440 1y ago
  But you need to, you know, actually float something in a text. I think to do it with flexbox/grid you need JS that calculates heights and than manually splits the text into boxes with heights, so essentially you are doing rendering. Also is there another way to position boxes side-by-side in an inline context without float?

mdaniel 1y ago

> A method that returns Optional<T> may return null. projects that do this drive me bananas If I had the emotional energy, I'd open a JEP for a new @java.lang.NonNullReference and any type annotated with it would be a compiler error to assign null to it public interface Alpha {} @java.lang.NonNullReference public interface Beta {} Alpha a = null; // ok Beta b = null; // compiler error javac will tolerate this Beta b; if (Random.randBoolean()) { b = getBeta(); } else { b = newBeta(); } but I would need to squint at the language specification to see if dead code elimination is a nicety or a formality Beta b; if (true) { b = getBeta(); } else { b = null; // I believe this will be elided and thus technically legal }

Spivak 1y ago
I question the wisdom of even having Optional<T> in a language with nulls. It would raise some eyebrows if a function in Python returned an Optional type object rather than T | None. You have to do a check either way unless you're doing some cute monad-y stuff.
- catlover76 1y ago
  I think I get what you mean, but it's confusing ofc, because Optional[T] is the older type annotation in Python for T | None But like, when it comes to unwrappable optional/result thingies, there are libs in Python to mimic that kind of behavior from Rust and functional languages.
- singron 1y ago
  Maybe this is cute monady stuff, but there isn't an equivalent to Optional<Optional<T>> with only null/None. You usually don't directly write that, but you might incidentally instantiate that type when composing generic code, or a container/function won't allow nulls.
  - charcircuit 1y ago
    In what context would you not want to treat Optional.of(null) and null as the same? It shouldn't be a big deal.

upghost 1y ago

> Unset variables. If DIR is unset, rm -rf $DIR/ becomes rm -rf /. Using set -u can make bash error when encountering unset variable. sweet mercy :O Someone call the Inquisition

AnimalMuppet 1y ago
Instead, say rm -rf $DIR That is, skip the trailing slash. Then if $DIR is not set, it becomes an invalid command, because no file names were supplied.
- Terr_ 1y ago
  Better to make the requirement explicit, instead of relying on the argument-parsing details of rm or some other command: # Default message $ rm -rf "${DIR:?}" bash: DIR: parameter null or not set # Custom message $ rm -rf "${DIR:?It is not set OMG}" bash: DIR: It is not set OMG
mdaniel 1y ago
This was a very famous Steam bug

OptionOfT 1y ago

> Some routers and firewall silently kill idle TCP connections without telling application. Some code (like HTTP client libraries, database clients) keep a pool of TCP connections for reuse, which can be silently invalidated. To solve it you can configure system TCP keepalive. For HTTP you can use Connection: keep-alive Keep-Alive: timeout=30, max=1000 header. Once a TCP connection has been established there is no state on routers in between the 2 ends of the connection. The issue here is firewalls / NAT entries timing out. And indeed, no RSTs are sent. We had the issue in K8s with the conntrack module set too low. Now, you can try to put in an HTTP Keep-Alive, but that will not help you. The HTTP Keep-Alive is merely for connection re-use at the HTTP level, i.e. it doesn't close the connection: https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Keep-Alive https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/... An HTTP Keep-Alive does not generate any packages, it merely postpones the close. A TCP Keep-Alive generates packages which resets the timers.

qouteall 1y ago
Thanks I will correct that
thwarted 1y ago
s/packages/packets/
altfredd 1y ago
Note that TCP Keep-Alive might not play well with mobile devices. Mobile operating systems can use application-level keep-alive packets, because those can be easily attributed to individual applications: an applications receives a TCP/UDP packet during low-power CPU sleep mode, asks system to wake up (by e.g. taking a wake-lock), and the system takes note who caused the wake-up. TCP Keep-Alive happens below application level, so it may be disabled, even when application can still be reached.

nayuki 1y ago

Largely a good listicle. Some feedback: > Unicode unification. Different characters in different language use the same code point. Different languages' font variants render the same code point differently. 語 This isn't a trap. The given example character means the same thing in Chinese and Japanese, and the Japanese version was imported from China. People from both languages recognize both font variants as the same conceptual character. The author is making it sound like the letter 'A' in English should have a different code point than an 'A' in French. Or that a lowercase 'a' with the top tail should be a different character than a lowercase 'a' without the top tail. Anyway, this is discussed at length in https://en.wikipedia.org/wiki/Han_unification https://en.wikipedia.org/wiki/Han_unification > There is a negative zero -0.0 which is different to normal zero. The negative zero equals zero when using floating point comparision. Normal zero is treated as "positive zero". And there are two ways to distinguish negative zero from normal zero: By their integer bit patterns, or by the fact that 1.0/-0.0 == -Inf vs. 1.0/0.0 == +Inf. > It's recommended to configure the server's time zone as UTC. Big yes. I use UTC for servers, logs, photos, and anything that is worth archiving and timestamping properly. Local time is only for colloquial use. > For integer (low + high) / 2 may overflow. A safer way is low + (high - low) / 2 Yes, but if low and high could be negative numbers, then you've just shifted the overflow to a different range. This matters for general binary search over an integer range, as opposed to unsigned binary search over an array. > C/C++ I'm going to throw in one of my lists of pitfalls - just using integer types and arithmetic correctly in C/C++ is a massive developer trap. That's like the most basic thing in programming. https://www.nayuki.io/page/summary-of-c-cpp-integer-rules https://www.nayuki.io/page/summary-of-c-cpp-integer-rules > Rebase can rewrite history "Can" is a weasel word; rebase does nothing but rewrite history.

cyberax 1y ago
> The author is making it sound like the letter 'A' in English should have a different code point than an 'A' in French. Or that a lowercase 'a' with the top tail should be a different character than a lowercase 'a' without the top tail. But we do have А and A. Even though they look the same. And unified Han characters are often quite distinct, it tripped me up as a learner of Chinese more than once. For example, a very common character '喝' (drink) looks quite a bit different: https://en.wiktionary.org/wiki/%E5%96%9D https://en.wiktionary.org/wiki/%E5%96%9D - they have a different number of strokes even. And I can't even copy-paste it here to demonstrate, because it changes form once I copy it from the Wikipedia article. Han unification is a mess.

gooodvibes 1y ago

> There are subtle differences between numpy and pytorch. This isn't really a trap, and it doesn't help anyone; it looks like "I got burned but I don't want to share the specifics".

busymom0 1y ago

> Division is much slower than multiplication (unless using approximation). Dividing many numbers with one number can be optimized by firstly computing reciprocal then multiply by reciprocal. Is this a general fact or specific to a language?

whobre 1y ago
It's generally true even for CPU instructions: https://electronics.stackexchange.com/questions/280673/why-does-hardware-division-take-much-longer-than-multiplication https://electronics.stackexchange.com/questions/280673/why-d...
ethan_smith 1y ago
It's hardware-level - division requires more CPU cycles than multiplication on most processor architectures, making this optimization pattern relevant across virtually all programming languages.

joshdavham 1y ago

> Python: - Default argument is a stored value that will not be re-created on every call. PSA for anyone working with datetime variables!

naet 1y ago
I'm not regularly a python developer and I just spent a ton of time earlier this week tripped up by the default argument being a stored value. I was using to make an empty set if no set was passed in... but the set was not always empty because it was being reused. Took me forever to figure out what was going on.

jonathrg 1y ago

> If you already use locking, no volatile needed. Kinda misleading. volatile is for memory mapped I/O and such. volatile means the memory access really happens

qouteall 1y ago
I changed the wording of it.

ikonst 1y ago

yaml: https://www.bram.us/2022/01/11/yaml-the-norway-problem/ https://www.bram.us/2022/01/11/yaml-the-norway-problem/ bash: errexit depends on caller's context, will utterly fail you one day: https://lists.gnu.org/archive/html/bug-bash/2012-12/msg00093.html https://lists.gnu.org/archive/html/bug-bash/2012-12/msg00093...

qouteall 1y ago
Added

DatDay 1y ago

LF vs CRLF

mdaniel 1y ago
Which is incredibly painful on Windows systems doing a git clone of shell scripts, since core.autocrlf is often helpful, but not for shell scripts, since it causes the weirdest looking error messages: MSYS$ cat build.sh #!/bin/bash echo "hello, world" MSYS$ ./build.sh : not found: 2: build.sh e.g. https://askubuntu.com/questions/370124/not-found-error-when-running-a-script-with-sh https://askubuntu.com/questions/370124/not-found-error-when-... Polite projects will have .gitattributes specifying that .sh or .bash or bin/* or whatever are to always checkout with eol=lf <https://git-scm.com/docs/gitattributes#_eol https://git-scm.com/docs/gitattributes#_eol> As best I can tell, .ps1 does tolerate Unix lf but I'd bet good money that .bat and .cmd definitely do not
qouteall 1y ago
Thanks for reminding. Added.

aragilar 1y ago

"Associativity law and distribution law doesn't strictly hold because of inaccuracy." should be due to precision loss not inaccuracy (they are different).

qouteall 1y ago
updated

nextworddev 1y ago

The biggest trap of all: building things that no one, including yourself, wants

geuis 1y ago
I would agree on the self part. But otherwise this point of view is distinctly in contrast with the recently republished "work on things that don't scale" article from pg. Also as a corollary, I was thinking about games from the 90s I spent hundreds of hours playing back then earlier today. Bolo and Escape Velocity in particular come to mind. They were "simple" games with immense depth. But after some fruitless searching, all I find is scattered questions and comments over the last few years looking for modern equivalents are a handful of recommendations for games that are no longer developed or are defunct. There's clear prior evidence of both success and lack of modern supply. Want to have a minimally minor successful game with established nostalgic audience? Make a new version of EV that is that game at its core. Don't be fancy, just do the thing Ambrosia did. Expand from there. The simple model is look forward, and also look back. The first itch is small. For yourself. Find some others with a similar itch. The hard part is pushing your idea into something more people want. That's where pg's 2013 article comes in to play. That's the hard part. But that leaves a huge space between 0 and 10 where someone can find a successful niche. Hell I've thought about trying to make a modern EV. It's tantalizing. But I've never made a game in my life. Ok I've rewritten Game of Life a lot. Good concept to try new ideas with. But the amount of work for a solo dev trying to recapture that original magic with no background in game dev is daunting.
- nextworddev 1y ago
  well if you at least build something you want, you are doing something that doesn't scale no?

chrismorgan 1y ago

Adjacent to the bit about 100vh, I’d add an item about the much older fundamental stupidity of viewport units, which Firefox tried to fix but no one else got on board and so they eventually removed their patch and went back to being as broken as everyone else. That is: they ignore scrollbars. Use a platform with 17px-wide scrollbars, and in a document with vertical scrolling, 100vw is now 100% of the viewport width… plus 17px. People get this wrong all the time, and it’s only increased as more platforms have switched to overlay scrollbars by default. > Blur does not consider ambient things. Need to make that backdrop blur. > Whitespace collapse. HTML Whitespace is Broken I always hated that article title. It’s not broken, it’s just different from what you occasionally expected, mostly for very good reasons that let it do what you expected most of the time. I also disagreed with some significant other parts of it: https://news.ycombinator.com/item?id=42971415 https://news.ycombinator.com/item?id=42971415. > Two concepts: code point (rune), grapheme cluster: I have problems with this lot. Firstly: add code units. When dealing with UTF-8 and you can access individual bytes, they’re UTF-8 code units. When dealing with UTF-16 and you can access 16-bit values, including surrogates, they’re UTF-16 code units. Secondly: don’t talk about code points in general, talk about scalar values, which are what code points would have been were it not for that accursèd abomination UTF-16. Specifically, scalar values excludes the surrogate code points. Sensible things work with scalar values. Python is the only thing I can think of that gets this wrong: its strings are sequences of code points, so you can represent lone surrogates (representable in neither UTF-8 nor UTF-16). This is so stupid. Thirdly: ditch the alias “rune”, Go invented it and it never caught on. I don’t know of anything else that uses the term (though maybe a few things do), and the term rune gets used for other unrelated things (e.g. in Svelte 5). > Some text files have byte order mark (BOM) at the beginning. For example, EF BB BF is a BOM that denotes the file is in UTF-8 encoding. It's mainly used in Windows. Some non-Windows software does not handle BOM. BOM was about endianness, and U+FEFF. Link to https://en.wikipedia.org/wiki/Byte_order_mark https://en.wikipedia.org/wiki/Byte_order_mark. It made sense in UTF-16 and UTF-32: for UTF-16, if the file starts with FE FF it’s UTF-16BE, if FF FE it’s UTF-16LE. UTF-8 application of it was always a mess, never really caught on, and I think can fairly be considered completely obsolete now: the typical person or software will never encounter it. Very little software will actually handle it any more. Fortunately, it doesn’t tend to matter much: U+FEFF is the BOM for a reason, it’s ZERO WIDTH NO-BREAK SPACE. > YAML: I’d add “disallows Tab indentation”. It’s the only thing I can immediately think of that’s like that. (Make is roughly the opposite, recipe lines having to start with a single Tab. Python doesn’t let you mix spaces and tabs. These are all I can immediately think of.)

decasia 1y ago

For what it's worth, I really enjoyed "Traceroute Isn't Real." I have noticed for quite a while that the data from it is at best patchy, often apparently meaningless. So it's helpful to see the explanation of why that is expected behavior: https://gekk.info/articles/traceroute.htm https://gekk.info/articles/traceroute.htm (If it's outdated I'm curious if anyone knows relevant updates?)