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feat: implement `last` and `lastOption` operators #26

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geminicaprograms merged 1 commit into master from feat_lastOption_last

Oct 30, 2023

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geminicaprograms commented Oct 26, 2023 •

edited

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The lastOption operator returns the last element in Source wrapped in Some or None in case when source is empty. Note that this is a terminal operation for source e.g.:

  Source.empty[Int].lastOption()  // None
  val s = Source.fromValues(1, 2)
  s.lastOption()                  // Some(2)
  s.receive()                     // ChannelClosed.Done

The last operator returns the last element in Source or throws NoSuchElementException in case when it is empty. In case when receive() fails with exception then this exception is re-thrown. It is also a terminal operation e.g.:

  Source.empty[Int].last()        // throws NoSuchElementException("cannot obtain last from an empty source")
  val s = Source.fromValues(1, 2)
  s.last()                        // 2
  s.receive()                     // ChannelClosed.Done

Note that ChannelClosedException.Error was improved to contain cause exception (if available).

geminicaprograms requested review from adamw, rucek and kciesielski

October 26, 2023 14:14

geminicaprograms self-assigned this

geminicaprograms commented

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core/src/main/scala/ox/channels/SourceOps.scala Outdated Show resolved Hide resolved

core/src/main/scala/ox/channels/SourceOps.scala Outdated Show resolved Hide resolved

core/src/main/scala/ox/channels/SourceOps.scala Outdated Show resolved Hide resolved

geminicaprograms force-pushed the feat_lastOption_last branch from 985c7f3 to 710a8ea Compare

October 27, 2023 10:42

geminicaprograms commented

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core/src/main/scala/ox/channels/ChannelClosed.scala Outdated Show resolved Hide resolved

geminicaprograms force-pushed the feat_lastOption_last branch from 710a8ea to abef2ed Compare

October 27, 2023 11:18

adamw reviewed

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core/src/main/scala/ox/channels/SourceOps.scala Outdated Show resolved Hide resolved

geminicaprograms force-pushed the feat_lastOption_last branch from abef2ed to d60ce81 Compare

October 27, 2023 13:37

geminicaprograms requested a review from adamw

October 27, 2023 13:38

geminicaprograms mentioned this pull request

chore: apply comments from #27 to existing code in SourceOps.scala #28

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geminicaprograms force-pushed the feat_lastOption_last branch from d60ce81 to 1200363 Compare

October 27, 2023 15:39

rucek reviewed

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core/src/main/scala/ox/channels/SourceOps.scala Outdated

+                def lastOption(): Option[T] =
+                  supervised {
+                    var value: Option[T] = None
+                    repeatUntil {

Contributor

rucek Oct 27, 2023

nitpick: In other operators we're using repeatWhile, which is similar, just with the condition inverted. I think we could use repeatWhile here as well for consistency.

Contributor Author

geminicaprograms Oct 30, 2023

🤷‍♂️ but turned to repeatWhile

core/src/main/scala/ox/channels/SourceOps.scala Outdated

@@ @@ -565,6 +565,63 @@ trait SourceOps[+T] { this: Source[T] => @@
                       case ChannelClosed.Error(r) => throw r.getOrElse(new NoSuchElementException("getting head failed"))
                       case t: T @unchecked        => t
                   }
+                /** Returns the last element from this source wrapped in [[Some]] or [[None]] when the source is empty. Note that `lastOption` is a

Contributor

rucek Oct 27, 2023

suggestion: According to the scaladoc style guide, please use "this source" instead of "[the] source" throughout the scaladoc. Also applies to the scaladoc for last.

Contributor Author

geminicaprograms Oct 30, 2023

Done

core/src/main/scala/ox/channels/SourceOps.scala Outdated

+                  * @return
+                  *   A `Some(last element)` if source is not empty or `None` otherwise.
+                  * @throws ChannelClosedException.Error
+                  *   When [[receive]] fails.

Contributor

rucek Oct 27, 2023

thought: receive (the function) is an implementation detail that the user might not be aware of. How about rephrasing this like "When receiving an element from this source fails."? Also applies to last

Contributor Author

geminicaprograms Oct 30, 2023

Done

core/src/main/scala/ox/channels/SourceOps.scala Outdated

+                  *   }
+                  *   }}}
+                  */
+                def last(): T = lastOption().getOrElse(throw new NoSuchElementException("cannot obtain last from an empty source"))

Contributor

rucek Oct 27, 2023

nitpick: Please use "last element" insted of "last" in the error message.

Contributor Author

geminicaprograms Oct 30, 2023

Done

core/src/main/scala/ox/channels/ChannelClosed.scala Show resolved Hide resolved

rucek mentioned this pull request

feat: implement fold operator #27

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adamw approved these changes

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          feat: implement last and lastOption operators

4f1d858

The `lastOption` operator returns the last element in `Source` wrapped in
`Some` or `None` in case when source is empty. Note that this is a terminal
operation for source e.g.:

  Source.empty[Int].lastOption()  // None
  val s = Source.fromValues(1, 2)
  s.lastOption()                  // Some(2)
  s.receive()                     // ChannelClosed.Done

The `last` operator returns the last element in `Source` or throws
`NoSuchElementException` in case when it is empty. In case when `receive()`
fails then `ChannelClosedException.Error` exception is thrown. It is also
a terminal operation e.g.:

  Source.empty[Int].last()        // throws NoSuchElementException("cannot obtain last element from an empty source")
  val s = Source.fromValues(1, 2)
  s.last()                        // 2
  s.receive()                     // ChannelClosed.Done

Note that ChannelClosedException.Error was improved to contain `cause`
exception (if available).

geminicaprograms force-pushed the feat_lastOption_last branch from 1200363 to 4f1d858 Compare

October 30, 2023 11:24

geminicaprograms requested a review from rucek

October 30, 2023 11:25

rucek approved these changes

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geminicaprograms merged commit 2cde6cd into master

geminicaprograms deleted the feat_lastOption_last branch

October 30, 2023 12:41

geminicaprograms added a commit that referenced this pull request


          chore: apply comments from #26 and #27 to existing code in `SourceOps…

4fc8379

….scala` (#28)

The following comments were applied:
* use supervised instead of scoped
* use toThrowable instead of ad-hoc exception creation
* don't catch exceptions in headOption
* also fixed comments about the source and receive function

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