On Mon, Apr 6, 2015 at 6:35 PM, Dmitry Soshnikov <dmitry.soshni...@gmail.com > wrote:
> On Mon, Apr 6, 2015 at 11:33 AM, Christoph Pojer < > christoph.po...@gmail.com> wrote: > >> Tim Yung and I have hacked on a reference implementation for the >> "Existential Operator" using esprima-fb and jstransform: "a?.b" >> >> Example: >> >> `a?.b` => `(a == null ? void 0 : a.b)` >> `a?.b.c` => `(a == null ? void 0 : a.b.c)` >> >> This must also make sure that `a` only gets evaluated a single time. >> >> Based on previous discussions on es-discuss and TC39, it seems that >> this was tabled for ES6. I think now is a good time to bring it up for >> ES7. There is precendence for this feature in other languages - it was >> recently added to C# and Hack and has always been in CoffeeScript. >> TypeScript is waiting for TC39: >> https://github.com/Microsoft/TypeScript/issues/16 >> >> In the past, this topic has invited a lot of bikeshedding, but I'd >> like us to look past this. Several communities within and outside the >> JS community have identified the need for this operator. My >> understanding is that a decision needs to be made about whether the >> operator should short-circuit additional invocations in the call chain >> if the operand is null (aka. null propagation). >> >> For example, if `a` is null, should `a?.b.c`: >> >> 1) evaluate to `(void 0).c` and throw a TypeError? >> 2) short-circuit at `a` and return `void 0`? >> >> It appears that C# chose option #2 whereas Hack and CoffeeScript chose >> option #1. Our current implementation chose option #1 > > > Hold on, I guess it's a typo, since as discussed in the internal > conversation, and based on the implementation, your current prototype > transform implements option (2). I.e. it's not yet compositional. > CoffeeScript also has option (2), and is not compositional, since: > > `a?.b.c` and `(a?.b).c` have different semantics in case if `a` is `null`. > > >> but we'd be >> happy to build a reference implementation for option #2. >> >> > Yeah, (2) will make it compositional. > > Err, option (1) I meant of course. Dmitry
_______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
