On Sun, Sep 6, 2015 at 11:54 PM, Andrea Faulds <a...@ajf.me> wrote: > Hi Bob, > > This has probably already come up, but I'd like to weigh in on the symbol > choice. > > On the subject of syntax, ~> (let's call it the squiggle arrow) seems like a > very poor choice compared to ==> (let's call it Hack's arrow). > > I think it's been mentioned that ==>, Hack's arrow, was thought to be likely > to be confused with =>, the key/value separator in array() and foreach(). > But I'd argue this is actually rather unlikely, for two reasons. > > The first of these is that ==> is a whole column wider. So, if there's a > smudge on the screen or something, you could still clearly distinguish ==> > from =>. They're visually distinct, much like =, == and === are, which I'm > sure any PHP programmer can tell apart. > > Second, => is only used in very limited contexts. You can't use => in a > normal expression or statement. You can't mistake ($t ==> $f ==> $t) for ($t > => $f => $t) for long, because the latter would never be a valid expression. > And in the contexts where => does work, it's unlikely you'd be using a > closure – at least, I can't think of a case where you'd want to create a > numeric array of closures using a literal. > > For those two reasons, I don't agree that confusing ==> with => would be a > big problem. > > Now ~>, the squiggle arrow, was supposedly chosen to reduce the likelihood > of confusion. However, I would argue that it is actually *more* likely to > cause confusion. In this case the potential confusion would be with ->, the > object property dereference operator. I have two reasons for why the two > operators would be confused, and they're the respective inverses of the > reasons why => and ==> wouldn't. > > First, ~> visually takes up the same amount of space as ->, so if you have a > small character size, a blurry or low-resolution screen, or poor eyesight, > there's nothing aside from the very slight curvature (and maybe syntax > highlighting, which does not yet exist) to distinguish ~> from ->. > > Second, ->, the object property dereference operator, is used in a wide > range of contexts. It's a valid expression (and thus statement), and so > would crop up in many places where ~>, the squiggle arrow, also would. A > realistic example of this is the Church Booleans, an encoding of the boolean > values "true" and "false" in the lambda calculus: "true" is a function that > takes two arguments and returns the first, and "false" is a function that > takes two arguments and returns the second. The "true" function would be > written, using squiggle arrows, as ($a ~> $b ~> $a). Now, if you squint, can > you tell that apart from ($a ~> $b -> $a)? Did you even notice the > difference in that second expression? (The second squiggle arrow become a > dereference operator.) I wouldn't be surprised if you didn't. And the > difference wouldn't always be immediately obvious from context. Here, the > unusual spacing might give it away (a variable property access would usually > be $b->$a), but not everyone is going to put spaces around their squiggle > arrows. > > For those two reasons alone, I think ~> is a poor choice. And that's without > the ugliness issue: in some fonts, particularly Japanese ones, ~ is rendered > at the top of the character box, like an overline. In such a font, ~> will > not look like an arrow. > > You did mention that the HHVM team might find things easier if you chose ~> > instead of ==>, given Hack already has ==>. Surely, though, that only > matters if ==> has different semantics in PHP and Hack, yet this proposal > matches Hack's implementation exactly, so far as I can tell. Also, it would > be nice if PHP and Hack don't diverge when implementing the same features, > unless there's a particularly good reason... it's not very kind to people > who use both languages. > > So, to conclude, I would urge you to change the RFC to use ==> instead of > ~>. > > Thanks. > > -- > Andrea Faulds > http://ajf.me/ > > > -- > PHP Internals - PHP Runtime Development Mailing List > To unsubscribe, visit: http://www.php.net/unsub.php >
Hello, these are all good points. Also, I realized it's definitely harder to write ~ than =. On my keyboard layout (Czech Qwerty) I have to do "right alt + shift + (key above Tab)". I'm not sure how it is with other non-US keyboard layouts, but it might be worth exploring before deciding on a symbol; or maybe there's a possibility that my keyboard layout is just an anomaly and you can write ~ on most keyboard layouts with a single key (or double). Regards PK -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
