<hr/>**评论：**<br/><br/>shovelpost: <pre><p>Sure it can: <a href="https://play.golang.org/p/-gF1qvNiUOy">https://play.golang.org/p/-gF1qvNiUOy</a></p></pre>mitchell-riley: <pre><p>what the fuck</p></pre>epiris: <pre><p>Unicode code points that look similar</p></pre>haskell_leghumper: <pre><p>If you look closely, those aren't a's, they're characters from the Canadian Aboriginal Syllabics block, which are allowed in Go identifiers. From Go's perspective, those are just three long identifiers. </p></pre>cheesechoker: <pre><p>Not sure <a href="/r/golang" rel="nofollow">/r/golang</a> will ever top that post. Legendary</p></pre>comrade_donkey: <pre><p>Not sure if allusion to generics joke. Have an upvote.</p>
<p>Edit: definitely generics joke right here.</p></pre>longtimedockhand: <pre><blockquote>
<p>a, ?, а</p>
</blockquote>
<p><a href="https://www.fileformat.info/info/unicode/char/0061/index.htm" rel="nofollow">U+0061 LATIN SMALL LETTER A</a></p>
<p><a href="https://www.fileformat.info/info/unicode/char/1d5ba/index.htm" rel="nofollow">U+1D5BA MATHEMATICAL SANS-SERIF SMALL A</a></p>
<p><a href="https://www.fileformat.info/info/unicode/char/0430/index.htm" rel="nofollow">U+0430 CYRILLIC SMALL LETTER A</a></p></pre>mashmorgan: <pre><p>OK, mind blown, can someone explain, so I can goto: sleep</p></pre>epiris: <pre><p>The variables themselves, the value inside the source each has a different unicode code point, i.e.: <a href="https://play.golang.org/p/bo9VnFnpNsW" rel="nofollow">play</a>. Unicode has some characters that look very similar, which has some interesting security consequences. I like to use this fact for unit tests in anything that does byte/string processing, since they are easy to spot the width of the rune and all can jump directly to the upper or lower bound of the a-zA-Z range. So you can write a base set of tests in ascii and then derive multi-width unit tests from them by adding the offsets of rune.</p>
<pre><code>const (
// Test unicode points I like to use for utf8, they all are a-z and do not
// have a step to alternative casing. Meaning they have the property that:
//
// (uwN) 'A' + 32 = 'a' (lower case mapped letter)
uw1 = 'A' // 0x41 65 (1 byte)
uw2 = 'À' // 0xC0 192 (2 bytes)
uw3 = 'Ａ' // 0xFF21 65313 (3 bytes)
uw4 = '?' // 0x1D400 119808 (4 bytes)
)
</code></pre></pre>mashmorgan: <pre><p>aaaarggggghhhhhhhhh .. of to bed !!!!!!!!!!!!!!!!!!!</p></pre>sacado: <pre><p>Fun but that's not really answering the main question (it's not the same "a").</p></pre>: <pre><p>[deleted]</p></pre>Momer: <pre><p>The shared-state race condition is the only way I could think of in Go as well.</p></pre>theonlycosmonaut: <pre><p>But don't goroutines only pre-empt each other except at well defined boundaries? Or has that changed? Could there be a data race in between expressions like that?</p>
<p>Looks like <a href="/u/nevyn" rel="nofollow">/u/nevyn</a> below has had to add manual yielding in a function call to achieve an approximation.</p></pre>dgryski: <pre><p>A sufficiently smart compiler could easily optimize that comparison to a constant <code>false</code>. Remember that a program with data races is not a valid program.</p></pre>: <pre><p>[deleted]</p></pre>dgryski: <pre><p>gcc is a sufficiently smart compiler, and gccgo has this optimization.</p>
<p>Undefined behaviour in C is a real problem because it's so easy to hit. The Go specification doesn't even mentioned 'undefined'. The Go compiler produces code that assumes there are no data races. I probably should have said "conforming program" instead of "valid program".</p></pre>jerf: <pre><p>It's not pointless. This is a legitimate source of bugs in languages with a lot of implicit, overridable behavior, and it's a valuable data point in the skill level of a programmer whether they know this, because it's probably because they've experienced it.</p></pre>: <pre><p>[deleted]</p></pre>jerf: <pre><p>I assume you've never used Ruby then? Check this sort of thing out: <a href="https://www.infoq.com/articles/ruby-open-classes-monkeypatching/">https://www.infoq.com/articles/ruby-open-classes-monkeypatching/</a></p>
<p>Yes, it's obviously stupid in isolation to do this sort of thing, but in the real world, "clever little things" add up. And hoo boy, was Ruby in love with clever little things for a while.</p>
<p>I've also personally seen bad things happen when I added an override to stringification in perl code. I've also seen people do some ill-advised things in Haskell overriding equality specifically, on <a href="/r/Haskell">/r/Haskell</a>.</p>
<p>If you're lucky enough not to have encountered this, well, be thankful for your luck. They can be viciously difficult bugs to track down when they don't produce crashes, and sometimes even then.</p></pre>: <pre><p>[deleted]</p></pre>epiris: <pre><p>I think the premise for his argument wasn't well formed, since I agree with you this condition would be a rare encounter. But I do agree with his argument that it isn't pointless, going through enough thought exercises exactly like this was what allowed you to draw a conclusion. Which enabled you to write two polite and helpful sentences for the OP, the trailing line had a hint of condescension which turned things contentious.</p></pre>sacado: <pre><p>If a candidate can answer OP's question (in languages where operators can be redefined, not in go), he will probably be able to find potential errors in custom equality operators.</p></pre>nevyn: <pre><p>Eh, wasn't sure if the compiler would optimize things away (maybe more likely in the original version). <a href="https://play.golang.org/p/QaNx44K_gx4" rel="nofollow">https://play.golang.org/p/QaNx44K_gx4</a></p>
<p>Doesn't work on play, but locally it works very quickly.</p></pre>dgryski: <pre><p>But blows in with the race detector. Use atomic loads instead. </p></pre>nevyn: <pre><p>Yeh, I wanted it as close as possible to the question.</p></pre>mcandre: <pre><p>Curious: Does Go allow overriding of equality according to some interface, as in C++, Java, Ruby, Haskell?</p>
<p>If so, implementing an EqualTo() or such could be specially implemented to return true for inputs 1, 2, 3, ...</p></pre>PaleocorticalWise: <pre><p>Go does not allow this.</p></pre>alasijia: <pre><p>it is possible for a not-well-written concurrent program, though the possibility is very low.</p></pre>faiface: <pre><p>Hey, I know everyone's gonna hate me now, but nonsense like this can never happen in functional programming!</p></pre>TheMerovius: <pre><p>My Haskell isn't amazing, but</p>
<pre><code>data Fnord = Fnord Integer
instance Num Fnord where
(Fnord a) + (Fnord b) = Fnord (a + b)
(Fnord a) * (Fnord b) = Fnord (a * b)
negate (Fnord a) = Fnord (negate a)
abs (Fnord a) = Fnord (abs a)
signum (Fnord a) = Fnord (signum a)
fromInteger = Fnord
instance Eq Fnord where
a == b = True
main = do
a <- return (Fnord 42)
print (a == 1 && a == 2 && a == 3)
return ()
</code></pre></pre>flogic: <pre><p>I would be careful with that. I don't think can exactly do this in Haskell, but you can play with the Eq type class for a custom type.</p></pre>faiface: <pre><p>Alright, you can possibly do that one, but you can't get this to work in Haskell:</p>
<pre><code>a == 1 && !(a == 1)
</code></pre>
<p>Which you can get in Go, JavaScript, etc.</p></pre>nhooyr: <pre><p>how can you get that in Go?</p></pre>faiface: <pre><p>Exactly as another comment described, by concurrency with shared variables and race conditions.</p></pre>nhooyr: <pre><p>That comment was deleted but I understand now, thanks.</p></pre>Koh_Phi_Phi: <pre><p>This particular problem has more to do with type safety than functional programming. For instance if you have the ability to define == as a function to always return true then functional programming doesn’t help you.</p></pre>justinisrael: <pre><p>Posted in response to this?
<a href="https://codeburst.io/javascript-can-a-1-a-2-a-3-ever-evaluate-to-true-aca13ff4462d" rel="nofollow">https://codeburst.io/javascript-can-a-1-a-2-a-3-ever-evaluate-to-true-aca13ff4462d</a></p>
<p>But Go doesn't allow operator overloading. </p></pre>
