Robert Sayre Reporter
	Description • 18 years ago

I'm pretty sure this a bug-- note the output of "5,6,9" at the end.

js> var list1 = [[1,2],[3,4],[5,6]];
js> var list2 = [[1,2,3],[4,5,6],[7,8,9]];
js> for each (var [foo, bar] in list1) {
    print(foo + "," + bar);
  }
1,2
3,4
5,6
js> for each (var [foo, bar, baz] in list2) {
    print(foo + "," + bar + "," + baz);
  }
1,2,3
4,5,6
7,8,9
js> function gen(list) {
    for each (var test in list) {
      yield test;
    }
  }
js> var iter1 = gen(list1);
js> for (var [foo, bar] in iter1) {
    print(foo + "," + bar);
  }
1,2
3,4
5,6
js> var iter2 = gen(list2);
js> for (var [foo, bar, baz] in iter2) {
    print(foo + "," + bar + "," + baz);
  }
typein:56: SyntaxError: invalid for/in left-hand side:
typein:56: for (var [foo, bar, baz] in iter2) {
typein:56: .........................^
js> 5,6,9
js>

	Brendan Eich [:brendan] Assignee
	Comment 1 • 18 years ago

Yes, bug -- for the enumeration case (where the object to the right of in is not an iterator), ES4 as proposed requires a length-2 pattern. For iteration (where the object to the right of in is an iterator and can return any value), there should be no such restriction.

/be

	Brendan Eich [:brendan] Assignee
	Comment 2 • 18 years ago

Enumeration destructures via [key, value], hence the restriction. The error check is in the parser currently, but it can't decide the type of the expression to the right of 'in', in general. So the draft ES4 spec should not specify SyntaxError; the destructuring enumeration error case (pattern other than array of length 2) must be a TypeError.

/be

	Brendan Eich [:brendan] Assignee
	Comment 3 • 17 years ago

ES4 proposal now says for ([key, value] in obj) is just a pair destructuring of the value returned by obj's iterator, by default the identifier string or Name if obj does not have a custom iterator::get. So sayrer's induction works as hoped, and anyone wanting the JS1.7-era key,value default enumeration will have to use for ([key, value] in iterator::items(obj)).

This bug should get fixed for 1.9 if possible, so the 1.7 experiment does not leak too far from the lab.

/be

	Brendan Eich [:brendan] Assignee
	Comment 4 • 17 years ago

In JS1.8, use for ([k,v] in Iterator(o)) instead of JS1.7's for ([k,v] in o). For JS2/ES4, we want iterator::items, but I'm not adding that or related APIs for 1.8.

/be

	Brendan Eich [:brendan] Assignee
	Comment 5 • 17 years ago

Fixed on trunk:

js/src/jsapi.c 3.322
js/src/jsparse.c 3.282

/be

	Bob Clary [:bc] (inactive)
	Comment 6 • 17 years ago

2007-05-27 13:13 mozilla/js/tests/browser.js 	                        1.3
2007-05-27 13:13 mozilla/js/tests/js1_7/geniter/regress-366941.js 	1.1
2007-05-27 13:13 mozilla/js/tests/js1_8/shell.js 	                1.4
2007-05-27 13:13 mozilla/js/tests/js1_8/regress/regress-366941.js 	1.1 

didn't include the Iterator(...) stuff since I wasn't clear on what was going on.

	Nickolay_Ponomarev
	Comment 8 • 17 years ago

This is mentioned on http://developer.mozilla.org/en/docs/New_in_JavaScript_1.7#Looping_across_objects and http://developer.mozilla.org/en/docs/New_in_JavaScript_1.8

	Bob Clary [:bc] (inactive)
	Comment 9 • 17 years ago

verified fixed 1.9.0 linux/mac*/windows.