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
[email protected]
Home: http://rauschma.de
Blog: http://2ality.com
On 01.04.2012, at 10:30, Dmitry Soshnikov<[email protected]> 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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