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List:       openjdk-openjfx-dev
Subject:    Re: RFR: 8274771: Map, FlatMap and OrElse fluent bindings for ObservableValue [v16]
From:       Kevin Rushforth <kcr () openjdk ! org>
Date:       2022-06-30 23:54:02
Message-ID: 4SyeeOKmJpOlJV_5pxkAn9fjjjUVLL84t7NYzoA--is=.2f8ca931-cf15-4cd9-a407-a0094373c930 () github ! com
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On Thu, 30 Jun 2022 06:57:03 GMT, John Hendrikx <jhendrikx@openjdk.org> wrote:

> > This is an implementation of the proposal in \
> > https://bugs.openjdk.java.net/browse/JDK-8274771 that me and Nir Lisker \
> > (@nlisker) have been working on.  It's a complete implementation including good \
> > test coverage.   
> > This was based on https://github.com/openjdk/jfx/pull/434 but with a smaller API \
> > footprint.  Compared to the PoC this is lacking public API for subscriptions, and \
> > does not include `orElseGet` or the `conditionOn` conditional mapping. 
> > **Flexible Mappings**
> > Map the contents of a property any way you like with `map`, or map nested \
> > properties with `flatMap`. 
> > **Lazy**
> > The bindings created are lazy, which means they are always _invalid_ when not \
> > themselves observed. This allows for easier garbage collection (once the last \
> > observer is removed, a chain of bindings will stop observing their parents) and \
> > less listener management when dealing with nested properties.  Furthermore, this \
> > allows inclusion of such bindings in classes such as `Node` without listeners \
> > being created when the binding itself is not used (this would allow for the \
> > inclusion of a `treeShowingProperty` in `Node` without creating excessive \
> > listeners, see this fix I did in an earlier PR: \
> > https://github.com/openjdk/jfx/pull/185) 
> > **Null Safe**
> > The `map` and `flatMap` methods are skipped, similar to `java.util.Optional` when \
> > the value they would be mapping is `null`. This makes mapping nested properties \
> > with `flatMap` trivial as the `null` case does not need to be taken into account \
> > in a chain like this: \
> > `node.sceneProperty().flatMap(Scene::windowProperty).flatMap(Window::showingProperty)`. \
> > Instead a default can be provided with `orElse`. 
> > Some examples:
> > 
> > void mapProperty() {
> > // Standard JavaFX:
> > label.textProperty().bind(Bindings.createStringBinding(() -> \
> > text.getValueSafe().toUpperCase(), text)); 
> > // Fluent: much more compact, no need to handle null
> > label.textProperty().bind(text.map(String::toUpperCase));
> > }
> > 
> > void calculateCharactersLeft() {
> > // Standard JavaFX:
> > label.textProperty().bind(text.length().negate().add(100).asString().concat(" \
> > characters left")); 
> > // Fluent: slightly more compact and more clear (no negate needed)
> > label.textProperty().bind(text.orElse("").map(v -> 100 - v.length() + " \
> > characters left")); }
> > 
> > void mapNestedValue() {
> > // Standard JavaFX:
> > label.textProperty().bind(Bindings.createStringBinding(
> > () -> employee.get() == null ? ""
> > > employee.get().getCompany() == null ? ""
> > > employee.get().getCompany().getName(),
> > employee
> > ));
> > 
> > // Standard JavaFX + Optional:
> > label.textProperty().bind(Bindings.createStringBinding(
> > () -> Optinal.ofNullable(employee.get())
> > .map(Employee::getCompany)
> > .map(Company::getName)
> > .orElse(""),
> > employee
> > ));
> > 
> > // Fluent: no need to handle nulls everywhere
> > label.textProperty().bind(
> > employee.map(Employee::getCompany)
> > .map(Company::getName)
> > .orElse("")
> > );
> > }
> > 
> > void mapNestedProperty() {
> > // Standard JavaFX:
> > label.textProperty().bind(
> > Bindings.when(Bindings.selectBoolean(label.sceneProperty(), "window", "showing"))
> > .then("Visible")
> > .otherwise("Not Visible")
> > );
> > 
> > // Fluent: type safe
> > label.textProperty().bind(label.sceneProperty()
> > .flatMap(Scene::windowProperty)
> > .flatMap(Window::showingProperty)
> > .orElse(false)
> > .map(showing -> showing ? "Visible" : "Not Visible")
> > );
> > }
> > 
> > Note that this is based on ideas in ReactFX and my own experiments in \
> > https://github.com/hjohn/hs.jfx.eventstream.  I've come to the conclusion that \
> > this is much better directly integrated into JavaFX, and I'm hoping this proof of \
> > concept will be able to move such an effort forward.
> 
> John Hendrikx has updated the pull request incrementally with five additional \
> commits since the last revision: 
> - Move private binding classes to com.sun.javafx.binding package
> - Add note to Bindings#select to consider ObservableValue#flatMap
> - Fix bug invalidation bug in FlatMappedBinding
> 
> Also fixed a secondary issue where the indirect source of the binding
> was unsubscribed and resubscribed each time its value was recomputed.
> 
> Add additional comments to clarify how FlatMappedBinding works.
> 
> Added test cases for these newly discovered issues.
> - Fix typos in LazyObjectBinding
> - Rename observeInputs to observeSources

This looks quite good now. I believe the API is ready to go. I did a little testing \
and want to do some more tomorrow, and then hope to finish my review. I left a couple \
comments / questions inline.

Two overall comments:

1. The doc changes in Bindings.java should be added to the Specification section in \
the CSR.


2. The copyright line for each new file should be:


 * Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.


with a comma after the year.

modules/javafx.base/src/main/java/com/sun/javafx/binding/FlatMappedBinding.java line \
2:

> 1: /*
> 2:  * Copyright (c) 2021 Oracle and/or its affiliates. All rights reserved.

That should be `2022,` with a comma after the year in addition to fixing the year.

modules/javafx.base/src/main/java/com/sun/javafx/binding/Subscription.java line 90:

> 88:      */
> 89:     static <T> Subscription subscribe(ObservableValue<T> observableValue, \
>                 Consumer<? super T> subscriber) {
> 90:         ChangeListener<T> listener = (obs, old, current) -> \
> subscriber.accept(current);

Maybe call `Objects.requireNonNull()` on `observableValue` and `subscriber` before \
creating the listener?

modules/javafx.base/src/main/java/com/sun/javafx/binding/Subscription.java line 110:

> 108:      */
> 109:     static Subscription subscribeInvalidations(ObservableValue<?> \
>                 observableValue, Runnable runnable) {
> 110:         Objects.requireNonNull(runnable);

Maybe also call `Objects.requireNonNull(observableValue)` here?

modules/javafx.base/src/main/java/javafx/beans/binding/Bindings.java line 443:

> 441:      * Since 19, it is recommended to use {@link \
>                 ObservableValue#flatMap(java.util.function.Function)}
> 442:      * to select a nested member of an {@link ObservableValue}.
> 443:      * </p>

This should be added to the CSR.

-------------

PR: https://git.openjdk.org/jfx/pull/675


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