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1.x: scan & reduce give javadoc about unsharing the initialValue #4063

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Jun 22, 2016
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1.x: scan & reduce give javadoc about unsharing the initialValue #4063

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38 changes: 34 additions & 4 deletions src/main/java/rx/Observable.java
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Original file line number Diff line number Diff line change
Expand Up @@ -7201,8 +7201,8 @@ public final Observable<T> rebatchRequests(int n) {
* that does a similar operation on lists.
* <dl>
* <dt><b>Backpressure Support:</b></dt>
* <dd>This operator does not support backpressure because by intent it will receive all values and reduce
* them to a single {@code onNext}.</dd>
* <dd>The operator honors backpressure of its downstream consumer and consumes the
* upstream source in unbounded mode.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code reduce} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
Expand Down Expand Up @@ -7238,10 +7238,24 @@ public final Observable<T> reduce(Func2<T, T, T> accumulator) {
* This technique, which is called "reduce" here, is sometimes called "aggregate," "fold," "accumulate,"
* "compress," or "inject" in other programming contexts. Groovy, for instance, has an {@code inject} method
* that does a similar operation on lists.
* <p>
* Note that the {@code initialValue} is shared among all subscribers to the resulting Observable
* and may cause problems if it is mutable. To make sure each subscriber gets its own value, defer
* the application of this operator via {@link #defer(Func0)}:
* <pre><code>
* Observable&lt;T> source = ...
* Observable.defer(() -> source.reduce(new ArrayList&lt;>(), (list, item) -> list.add(item)));
*
* // alternatively, by using compose to stay fluent
*
* source.compose(o ->
* Observable.defer(() -> o.reduce(new ArrayList&lt;>(), (list, item) -> list.add(item)))
* );
* </code></pre>
* <dl>
* <dt><b>Backpressure Support:</b></dt>
* <dd>This operator does not support backpressure because by intent it will receive all values and reduce
* them to a single {@code onNext}.</dd>
* <dd>The operator honors backpressure of its downstream consumer and consumes the
* upstream source in unbounded mode.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code reduce} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
Expand Down Expand Up @@ -8167,7 +8181,23 @@ public final Observable<T> scan(Func2<T, T, T> accumulator) {
* <p>
* Note that the Observable that results from this method will emit {@code initialValue} as its first
* emitted item.
* <p>
* Note that the {@code initialValue} is shared among all subscribers to the resulting Observable
* and may cause problems if it is mutable. To make sure each subscriber gets its own value, defer
* the application of this operator via {@link #defer(Func0)}:
* <pre><code>
* Observable&lt;T> source = ...
* Observable.defer(() -> source.scan(new ArrayList&lt;>(), (list, item) -> list.add(item)));
*
* // alternatively, by using compose to stay fluent
*
* source.compose(o ->
* Observable.defer(() -> o.scan(new ArrayList&lt;>(), (list, item) -> list.add(item)))
* );
* </code></pre>
* <dl>
* <dt><b>Backpressure:</b></dt>
* <dd>The operator honors backpressure.</dd>
* <dt><b>Scheduler:</b></dt>
* <dd>{@code scan} does not operate by default on a particular {@link Scheduler}.</dd>
* </dl>
Expand Down