HN: the good parts

HN comments are terrible. On any topic I’m informed about, the vast majority of comments are pretty clearly wrong. Most of the time, there are zero comments from people who know anything about the topic and the top comment is reasonable sounding but totally incorrect. Additionally, many comments are gratuitously mean. You'll often hear mean comments backed up with something like "this is better than the other possibility, where everyone just pats each other on the back with comments like 'this is great'", as if being an asshole is some sort of talisman against empty platitudes. I've seen people push back against that; when pressed, people often say that it’s either impossible or inefficient to teach someone without being mean, as if telling someone that they're stupid somehow helps them learn. It's as if people learned how to explain things by watching Simon Cowell and can't comprehend the concept of an explanation that isn't littered with personal insults. Paul Graham has said, "Oh, you should never read Hacker News comments about anything you write”. Most of the negative things you hear about HN comments are true. And yet, I haven’t found a public internet forum with better technical commentary. On topics I'm familiar with, while it's rare that a thread will have even a single comment that's well-informed, when those comments appear, they usually float to the top. On other forums, well-informed comments are either non-existent or get buried by reasonable sounding but totally wrong comments when they appear, and they appear even more rarely than on HN. By volume, there are probably more interesting technical “posts” in comments than in links. Well, that depends on what you find interesting, but that’s true for my interests. If I see a low-level optimization comment from nkurz, a comment on business from patio11, a comment on how companies operate by nostrademons, I almost certainly know that I’m going to read an interesting comment. There are maybe 20 to 30 people I can think of who don’t blog much, but write great comments on HN and I doubt I even know of half the people who are writing great comments on HN1. I compiled a very abbreviated list of comments I like because comments seem to get lost. If you write a blog post, people will refer it years later, but comments mostly disappear. I think that’s sad -- there’s a lot of great material on HN (and yes, even more not-so-great material). What’s the deal with MS Word’s file format? Basically, the Word file format is a binary dump of memory. I kid you not. They just took whatever was in memory and wrote it out to disk. We can try to reason why (maybe it was faster, maybe it made the code smaller), but I think the overriding reason is that the original developers didn't know any better. Later as they tried to add features they had to try to make it backward compatible. This is where a lot of the complexity lies. There are lots of crazy workarounds for things that would be simple if you allowed yourself to redesign the file format. It's pretty clear that this was mandated by management, because no software developer would put themselves through that hell for no reason. Later they added a fast-save feature (I forget what it is actually called). This appends changes to the file without changing the original file. The way they implemented this was really ingenious, but complicates the file structure a lot. One thing I feel I must point out (I remember posting a huge thing on slashdot when this article was originally posted) is that 2 way file conversion is next to impossible for word processors. That's because the file formats do not contain enough information to format the document. The most obvious place to see this is pagination. The file format does not say where to paginate a text flow (unless it is explicitly entered by the user). It relies of the formatter to do it. Each word processor formats text completely differently. Word, for example famously paginates footnotes incorrectly. They can't change it, though, because it will break backwards compatibility. This is one of the only reasons that Word Perfect survives today -- it is the only word processor that paginates legal documents the way the US Department of Justice requires. Just considering the pagination issue, you can see what the problem is. When reading a Word document, you have to paginate it like Word -- only the file format doesn't tell you what that is. Then if someone modifies the document and you need to resave it, you need to somehow mark that it should be paginated like Word (even though it might now have features that are not in Word). If it was only pagination, you might be able to do it, but practically everything is like that. I recommend reading (a bit of) the XML Word file format for those who are interested. You will see large numbers of flags for things like "Format like Word 95". The format doesn't say what that is -- because it's pretty obvious that the authors of the file format don't know. It's lost in a hopeless mess of legacy code and nobody can figure out what it does now. Fun with NULL Here's another example of this fine feature: #include <stdio.h> #include <string.h> #include <stdlib.h> #define LENGTH 128 int main(int argc, char **argv) { char *string = NULL; int length = 0; if (argc > 1) { string = argv[1]; length = strlen(string); if (length >= LENGTH) exit(1); } char buffer[LENGTH]; memcpy(buffer, string, length); buffer[length] = 0; if (string == NULL) { printf("String is null, so cancel the launch.\n"); } else { printf("String is not null, so launch the missiles!\n"); } printf("string: %s\n", string); // undefined for null but works in practice #if SEGFAULT_ON_NULL printf("%s\n", string); // segfaults on null when bare "%s\n" #endif return 0; } nate@skylake:~/src$ clang-3.8 -Wall -O3 null_check.c -o null_check nate@skylake:~/src$ null_check String is null, so cancel the launch. string: (null) nate@skylake:~/src$ icc-17 -Wall -O3 null_check.c -o null_check nate@skylake:~/src$ null_check String is null, so cancel the launch. string: (null) nate@skylake:~/src$ gcc-5 -Wall -O3 null_check.c -o null_check nate@skylake:~/src$ null_check String is not null, so launch the missiles! string: (null) It appear that Intel's ICC and Clang still haven't caught up with GCC's optimizations. Ouch if you were depending on that optimization to get the performance you need! But before picking on GCC too much, consider that all three of those compilers segfault on printf("string: "); printf("%s\n", string) when string is NULL, despite having no problem with printf("string: %s\n", string) as a single statement. Can you see why using two separate statements would cause a segfault? If not, see here for a hint: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=25609 How do you make sure the autopilot backup is paying attention? Good engineering eliminates users being able to do the wrong thing as much as possible. . . . You don't design a feature that invites misuse and then use instructions to try to prevent that misuse. There was a derailment in Australia called the Waterfall derailment [1]. It occurred because the driver had a heart attack and was responsible for 7 deaths (a miracle it was so low, honestly). The root cause was the failure of the dead-man's switch. In the case of Waterfall, the driver had 2 dead-man switches he could use - 1) the throttle handle had to be held against a spring at a small rotation, or 2) a bar on the floor could be depressed. You had to do 1 of these things, the idea being that you prevent wrist or foot cramping by allowing the driver to alternate between the two. Failure to do either triggers an emergency brake. It turns out that this driver was fat enough that when he had a heart attack, his leg was able to depress the pedal enough to hold the emergency system off. Thus, the dead-man's system never triggered with a whole lot of dead man in the driver's seat. I can't quite remember the specifics of the system at Waterfall, but one method to combat this is to require the pedal to be held halfway between released and fully depressed. The idea being that a dead leg would fully depress the pedal so that would trigger a brake, and a fully released pedal would also trigger a brake. I don't know if they had that system but certainly that's one approach used in rail. Either way, the problem is equally possible in cars. If you lose consciousness and your foot goes limp, a heavy enough leg will be able to hold the pedal down a bit depending on where it's positioned relative to the pedal and the leverage it has on the floor. The other major system I'm familiar with for ensuring drivers are alive at the helm is called 'vigilance'. The way it works is that periodically, a light starts flashing on the dash and the driver has to acknowledge that. If they do not, a buzzer alarm starts sounding. If they still don't acknowledge it, the train brakes apply and the driver is assumed incapacitated. Let me tell you some stories of my involvement in it. When we first started, we had a simple vigi system. Every 30 seconds or so (for example), the driver would press a button. Ok cool. Except that then drivers became so hard-wired to pressing the button every 30 seconds that we were having instances of drivers falling asleep/dozing off and still pressing the button right on every 30 seconds because it was so ingrained into them that it was literally a subconscious action. So we introduced random-timing vigilance, where the time varies 30-60 seconds (for example) and you could only acknowledge it within a small period of time once the light started flashing. Again, drivers started falling asleep/semi asleep and would hit it as soon as the alarm buzzed, each and every time. So we introduced random-timing, task-linked vigilance and that finally broke the back of the problem. Now, the driver has to press a button, or turn a knob, or do a number of different activities and they must do that