arrow function syntax simplified

Quildreen Motta quildreen at gmail.com
Sun Apr 1 08:07:16 PDT 2012


Is there any particular reason optionally dynamic `this' got ditched 
from the current arrow syntax proposal? It's one thing that, I think, 
would make it more useful than just being used for inline callbacks.

Plus, with a syntax like:

---
let ps = { lookahead: (this, n) => { this.current().slice(0, n || 1) }
, current: (this) => { this.text.slice(this.offset) }
, move: (this, n) => { this.clone(this.text, this.offset + 1) }
, clone: (this, text, offset) => { let r = Object.create(this)
, r.offset = offset || 0
, r.text = text || '' }
}
---

You'd perhaps avoid some of the confusion on dynamic `this' by making it 
explicit that `this' is just an additional parameter passed over to the 
function — albeit implicitly. It seems to work for Python, though there 
`self' is bound at the instantiation time.


On 01/04/12 05:47, Axel Rauschmayer wrote:
> AFAIKT, Crockford is referring to an older version of the proposal.
>
>
> [[[Sent from a mobile device. Please forgive brevity and typos.]]]
>
> Dr. Axel Rauschmayer
> axel at rauschma.de
> Home: http://rauschma.de
> Blog: http://2ality.com
>
> On 01.04.2012, at 10:30, Dmitry Soshnikov<dmitry.soshnikov at gmail.com>  wrote:
>
>> Oh, wait, just have read Crock's article on =>  functions. A Python's style of passing manual `this'? That's interesting (why it's not specified on the wiki? where Crockford took it from? did you discuss it in a close ECMA meeting?). Inconsistent again with other functions.
>>
>> So, let's see, overall we have .. 6 types of functions in JS, and all have their own specific features. That's again interesting, if won't cause confusion.
>>
>> Dmitry
>>
>>
>> On Apr 1, 2012, at 1:13 AM, Dmitry Soshnikov wrote:
>>
>>> On Apr 1, 2012, at 12:34 AM, Axel Rauschmayer wrote:
>>>
>>>>>> Ah, good. But one can use the above (pseudo-)desugaring to predict the behavior of arrow functions, right? That is, there is no observable difference.
>>>>> There is, again, the difference in terms of delegation to the target's [[Construct]] in case of a bound function, see the spec ("bound" per ES5, of course, since, as Brendan notices, it's not just a syntactic sugar, but a new special type of functions).
>>>> OK. Ignoring [[Construct]] and .prototype, any other differences?
>>> Well, "ES5-bounds" also do not have `prototype' property, but delegate to the target's `prototype'. However, yes, there is the (main) difference in respect of supporting TCP (if I understand correctly, since had no time to follow the complete thread) -- return and break/continue jumps to the parent frame instead of working with the function itself.
>>>
>>> Lexical `this' is the only similar thing to bound functions, so we should not call =>  functions as synonym to bound functions. You may say, =>  function _as well as_ a bound captures `this' lexically, but in contrast with it, it has other features.  In my later analysis, I'll specify them as a new type of functions --  AF (Arrow Function) -- in addition to FE, FD, NFE, BF, etc., with many own features, but not just a syntactic sugar -- neither for FE, nor for BF.
>>>
>>> Dmitry
>>>
>>
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