I'm concerned that my r13731 change that sets the initial value of
constrained attributes to `undefined` rather than `null` may have more
fallout. This change by André fixes one instance, but there could be
many more lurking.
The issue: Constraints run in random order. Constraints that depend
on attributes that are themselves constrained may reference those
attributes when they are still undefined. When used in a numeric
expression, undefined coerces to NaN. NaN's are "sticky", hence may
pollute other attributes, and the constraint system may never recover.
r13731 was an attempt to make events fire less often by not having
them fire when a constraint updated an attribute to the value it
already had. To do this I needed a sentinel value that indicated that
the attribute had _never_ been updated (to distinguish the case where
a constraint was setting the attribute to `null`). `undefined` seemed
to fit that bill, but clearly it has additional consequences, as seen
in LPP-8088.
I'm looking for a way to achieve the optimization of 13731 without the
NaN hazard. I think this means that we have to revert to storing
`null` as the initial value of constrained attributes (even better
would be to store some type-correct equivalent of null). And we'll
have to have some sort of a flag that says you always send the event
the first time around (e.g., when called from __LZapplyArgs).
On 2009-05-11, at 08:55EDT, P T Withington wrote:
Approved as a work-around, but I think there may be a deeper issue
here...
On 2009-05-10, at 18:58EDT, André Bargull wrote:
Change 20090511-bargull-Yq7 by barg...@dell--p4--2-53 on 2009-05-11
00:08:07
in /home/Admin/src/svn/openlaszlo/trunk
for http://svn.openlaszlo.org/openlaszlo/trunk
Summary: constraint returns NaN in resizestatemin
New Features:
Bugs Fixed: LPP-8088 (DHTML: many warnings from
applyConstraintMethod())
Technical Reviewer: ptw
QA Reviewer: (pending)
Doc Reviewer: (pending)
Documentation:
Release Notes:
Details:
Default resize_min_width(height) to zero because if width/height
gets set to NaN all sorts of bad side effects were triggered.
For example using lps/components/incubator/test/opttree/test.lzx:
If you click on the resizer, images are reloaded from the server
and the scrollbar looks broken. This doesn't happen any longer
after applying the patch.
Tests:
Files:
M lps/components/utils/states/resizestatemin.lzx
Changeset: http://svn.openlaszlo.org/openlaszlo/patches/20090511-bargull-Yq7.tar
