Re: Default iterator
On Jun 20, 2012, at 9:37 PM, Erik Arvidsson wrote:
In our previous discussion I had come to the understanding that the
default iterator would use a private name. The main benefit for using
a private name is to not pollute the property name space.
import iterator from '@iter';
myObject[iterator] = function*() { ... };
If this was the ordinary property, iterator, it might break existing
code that already use iterator in some other way.
That was originally decided when we were using it to modify the behavior of
for-in loops, but since then we decided to leave for-in alone and create for-of
instead. This changes the cost trade-offs. Since for-of is a new thing under
the sun, the idea is that you should only use it for objects that are known to
be iterable -- because otherwise it throws. Objects are not iterable by default
(in particular, Object.prototype.iterator doesn't exist).
So the chance/cost of potential name conflicts is much lower than it was when
the iterator protocol extended for-in, because there it would cause existing
loops, that weren't written with iterators in mind, to break.
var obj = LibraryX.getObject();
obj.iterator().forEach(...);
Maybe a better example is a non-thunk obj.iterator. But this is probably
relatively rare, and you just wouldn't use obj in a for-of loop. You could
either change the existing API or compatibly add a new iterable property like
obj.elements.
It also breaks objects as maps since any string can be used as key.
It doesn't really break, it just means you shouldn't use them as iterables. But
keys(obj), vals(obj), items(obj) are better anyway since they let you pick
which things you want to iterate over. Also Map.
Dave
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Re: Default iterator
On Wed, Jun 20, 2012 at 11:37 PM, Erik Arvidsson
erik.arvids...@gmail.com wrote:
In our previous discussion I had come to the understanding that the
default iterator would use a private name. The main benefit for using
a private name is to not pollute the property name space.
Can you give an example of code that would be harmed by this pollution?
It's not pollution to add a useful method to Array.prototype. ES5 added several.
If this was the ordinary property, iterator, it might break existing
code that already use iterator in some other way.
var obj = LibraryX.getObject();
obj.iterator().forEach(...);
This code won't break.
If anything the new proposal makes it easier to change LibraryX to
support iteration: just add a suitable next() method to its iterator
object.
It also breaks objects as maps since any string can be used as key.
Again, please give an example of code that would break.
Note that the decision was already made that there would not be an
iterator method on Object.prototype, so objects-as-maps will be
iterated using a helper function:
var obj = JSON.parse(data);
import keys, items from '@iter';
for (let k of keys(obj)) { ... }
for (let [k, v] of items(obj)) { ... }
-j
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Re: Default iterator
On Jun 20, 2012, at 9:37 PM, Erik Arvidsson wrote: Jason Orendorff updated the iterator proposal a bit. Thank you Jason. I'd like to point out an issue with it though. In our previous discussion I had come to the understanding that the default iterator would use a private name. The main benefit for using a private name is to not pollute the property name space. Well, the ES6 spec. draft uses a private name, so I don't know if editing the wiki proposal will have any effect :-) If somebody things the spec should change there probably should have a bug filed against it and a subsequent discussion. ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
Default iterator
Jason Orendorff updated the iterator proposal a bit. Thank you Jason.
I'd like to point out an issue with it though.
In our previous discussion I had come to the understanding that the
default iterator would use a private name. The main benefit for using
a private name is to not pollute the property name space.
import iterator from '@iter';
myObject[iterator] = function*() { ... };
If this was the ordinary property, iterator, it might break existing
code that already use iterator in some other way.
var obj = LibraryX.getObject();
obj.iterator().forEach(...);
It also breaks objects as maps since any string can be used as key.
--
erik
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