Re: [RFC]Discuss] Syntax for Arrow Functions

On Tue, 30 May 2017, Levi Morrison wrote: > Internals, > > The previous discussion thread has died down significantly and so I'd > like to start a new one to refocus. This message has some redundant > information by design so people don't have to reference the other > thread so much. > > Based on the discussion there are a few different syntax choices > people liked. Overall it's a feature that people seem to want but > everyone seems to prefer a different syntax choice. > > 1. fn(params) => expr > 2. function(params) => expr > > 3. (params) ==> expr > 4. (params) => expr > > Note that 3 and 4 require a more powerful grammar and parser and that > 4 has ambiguities. I think we can work around them by rules -- only > mentioning it because its popular because of JavaScript and do not > prefer this at all. > > Note that 1 requires a new keyword. > > Option 2 looks the best from that perspective but is by far the > longest; remember people are partially interested in this feature > because they want shorter closures which this doesn't really help. > > This is why everyone is so divisive. All options have drawbacks. > Additionally some people don't like binding by value and would prefer > ref, and others really would be against by-ref. > > Which brings me to an option I don't think was ever discussed on list: > > 5. > [](params) => expr // binds no values > [=](params) => expr // binds by value > [&](params) => expr // binds by reference > > It has quite a few good qualities: > > - No new keywords > - Can choose between reference and value > - Concise > - Has precedence in C++, a major language > - Can be done in our existing grammar and parser[1] > - Can be extended to allow explicit binding of variables: > // all equivalent > // y is bound by value, array by reference > [&, $y]($x) => $array[] = $x + $y > [=, &$array]($x) => $array[] = $x + $y > > And of course it does have downsides: > > - Symbol soup (it uses a lot of symbols) > - A minor BC break. Empty arrays which are invoked as functions are > currently guaranteed to be errors at runtime and would have a new > valid meaning. Here's an example from inside an array literal: > > // error at runtime previously > [ []($x) => $x ] > // now an array with one item which is a closure that returns > its parameter > > Sara pointed out that we'd need to keep a leading = or > & in the > array to disambiguate from our array closure form. > > Overall I'd prefer 1 or 5. What do you guys think? I think 5 is terrible from a readability point of view. As you said it: "symbol soup". For a similar reason, I would discount 1 as being too vague. And hence would prefer 2, but I'm not actually convinced about this feature at all. cheers, Derick -- https://derickrethans.nl | https://xdebug.org | https://dram.io Like Xdebug? Consider a donation: https://xdebug.org/donate.php twitter: @derickr and @xdebug