Proper dispatch in the presence of optional arguments.

Proper dispatch in the presence of optional arguments.

Formerly for the methods like foo([Optional] x, [Opional] y), the following
dispatcher was emitted:

foo([x = _null, y = _null]) {
  if (y === _null) {
    return _foo_1(x);  // WRONG!
  }
  if (x === _null) {
    return _foo_2();
  }
  return _foo_3(x, y);
}

Now correct code is emitted:

foo([x = _null, y = _null]) {
  if (y !== _null) {
    return _foo_1(x, y);
  }
  if (x !== _null) {
    return _foo_2(x);
  }
  return _foo_3();
}

TBR=podivilov@chromium.org
BUG=4487
Committed: https://code.google.com/p/dart/source/detail?r=10661

[Anton Muhin, 2012-08-14 18:14:29]

I'd appreciate proper review.

[podivilov, 2012-08-21 13:46:57]

https://chromiumcodereview.appspot.com/10832300/diff/1/lib/dom/scripts/system...
File lib/dom/scripts/systemnative.py (right):

https://chromiumcodereview.appspot.com/10832300/diff/1/lib/dom/scripts/system...
lib/dom/scripts/systemnative.py:663: # complicated case.  Consider foo(x,
[Optional] y, [Optional=DefaultIsNullString] z)
I think it's exactly the optional in the middle problem we had previously since
[Optional=DefaultIsNullString] is mandatory in dart (they finally found a
loophole to introduce opt in the middle again :). Could you please clarify the
comment to state it more explicitly?

Another problem is that foo(x, y) will invoke fooNativeCallback(x, y, _null)
instead of fooNativeCallback(x, y, null).

[Anton Muhin, 2012-08-21 18:14:33]

https://chromiumcodereview.appspot.com/10832300/diff/1/lib/dom/scripts/system...
File lib/dom/scripts/systemnative.py (right):

https://chromiumcodereview.appspot.com/10832300/diff/1/lib/dom/scripts/system...
lib/dom/scripts/systemnative.py:663: # complicated case.  Consider foo(x,
[Optional] y, [Optional=DefaultIsNullString] z)
Yes, this _null/null distinction is another of problems I spotted in our current
code.

Updating a description...

On 2012/08/21 13:46:57, podivilov wrote:
> I think it's exactly the optional in the middle problem we had previously
since
> [Optional=DefaultIsNullString] is mandatory in dart (they finally found a
> loophole to introduce opt in the middle again :). Could you please clarify the
> comment to state it more explicitly?
> 
> Another problem is that foo(x, y) will invoke fooNativeCallback(x, y, _null)
> instead of fooNativeCallback(x, y, null).