pkg:observe -- implement dirty-checking fallback for non-observable objects

[DartBot]

Issue by jmesserly Originally opened as dart-lang/sdk#16342

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After landing https://codereview.chromium.org/132403010/ we'll have most of the infrastructure to do this.

Ideal:

• Users can get dirty checking for all objects, and faster change notification if the object supports it.

* Ideal: @­observable transform does not require ChangeNotifier base class.

* Need a way of marking an object @­observable in another library.

* Do we need an object to be a ChangeNotifier and have some properties dirty-checked? If so, we need a way of attempting to subscribe, and determining if such a property is not available for subscription. I think we need this to make computed properties really easy to use. Alternatively we can throw an error in this case so user at least knows that they forgot to make a property @­observable.

* remove Observable base class -- objects can be observed via PathObserver/CompoundObserver. Add ObjectObserver from observe-js

* ObservableList still provided as the "fast version"

* Add logging/tracing diagnostics about dirty checking to provide developers a way to assess performance impact of dirty checking -- how many objects, which objects, how often was dirty checking run and how long did it take?

* For best performance, this should be combined with an approach that generates fast-paths for expressions found in HTML

* For now, the @­observable transform will not be run in dev mode, meaning those objects will be treated as dirty-checked. If using "pub serve" the transform will happen automatically.

Any flaws in this plan? We've tried this before and not succeeded. I think the big changes since we last looked at this:

• pub build is here and pub serve is coming
• Zones have solved the issue of dirty-checking being triggered unreliably
• we now understand 'pkg:observe' is a package and does not need to ever be 'dart:observe'
• mirrors are now acceptable to use and we have other ways of mitigating their performance impact (generate fast-paths for html exprs)
• this is one of the two reasons users are still stuck on polymer 0.4 (pkg:web_ui). many prefer pkg:web_ui as well as angular.dart for this very reason

[DartBot]

Comment by anders-sandholm

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Removed Library-Observe label. Added Pkg-Observe label.

[DartBot]

Comment by jmesserly

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if we don't do this, we'll need to fix computed properties.

[DartBot]

Comment by jmesserly

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s/fix/make easier ...

[DartBot]

Comment by jmesserly

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Issue #40 has been merged into this issue.

[DartBot]

This comment was originally written by joo....@gmail.com

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yes, list and map work in web_ui fine, but on polymer has not reached the expected results, never.

[DartBot]

Comment by jmesserly

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Removed Area-Polymer label. Added Area-Pkg label.

[DartBot]

Comment by sigmundch

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Added this to the Later milestone. Removed Priority-Unassigned label. Added Priority-Medium label.

[DartBot]

Comment by sigmundch

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Added Polymer-P-2 label.

[DartBot]

Comment by sigmundch

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Removed this from the Later milestone.

[DartBot]

Comment by jmesserly

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IMO, should be higher priority... it's a big usability disadvantage compared with other systems.

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Removed Priority-Medium, Polymer-P-2 labels. Added Priority-High label.

[DartBot]

Comment by sethladd

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High Pri means we have a milestone assigned. Does this mean you're signing up to make it happen in 1.6? :)

[DartBot]

Comment by jmesserly

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@Seth -- Sadly no, am not working on this feature area anymore.

[DartBot]

Comment by sigmundch

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Since packages have an independent release cycle than the SDK, I don't want to assign any Milestone (it just confuses everyone).

This is important, there are many other things with higher priority for now, so I doubt we'll get to this that soon.

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Added Polymer-P-2 label.

[DartBot]

Comment by sigmundch

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Removed Polymer-P-2 label. Added Polymer-Milestone-Later label.

[DartBot]

Comment by sigmundch

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Removed Polymer-Milestone-Later label. Added PolymerMilestone-Later label.

[DartBot]

Comment by sethladd

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Bumping Priority.

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Removed Priority-High label. Added Priority-Medium label.

[DartBot]

Comment by blois

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It would be great if there were some way to ensure that dirty-checking does not creep into a codebase unexpectedly. From experience in large XAML apps which had a similar slow-path for non-observables we had to have a strict 'must never use the slowpath' rule, but did not have a decent way of enforcing it.

It's a bit tricky because the final component of a binding path may support observing while intermediate steps do not (or the reverse).

This could potentially be mitigated by tools for inspecting binding state of a DOM tree, but as a dev I'd prefer to be able to prevent this entirely.

[DartBot]

Comment by jmesserly

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Jake/Siggi, does this seem worth it? if so I can move this to the github tracker, otherwise let's close

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cc @jakemac53. cc @sigmundch.

[DartBot]

Comment by jakemac53

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lets close imo