Add extension methods to package:collection. #135

lrhn · 2020-05-13T13:36:03Z

Add a number of useful extension methods to List and Iterable, and to a few other types.

A good part of these extensions are backed by the algorithms of algorithms.dart, which is expanded to support them:

Added quickSort.
Add extra optional Random argument to shuffle.
Generalize some of the functions in algorithms.dart to work on specific properties of the objects (binarySearchBy,
lowerBoundBy, insertionSortBy, quickSortBy, mergeSortBy).

lrhn · 2020-05-13T13:37:10Z

This is a first crack at adding extension methods to package:collection.

They are not tested. Some are probably not useful (I expect Iterable<T extends num>.sum() to be mostly speculative).

natebosch

Did something get lost in the upload? There are no extension methods added here. This does look like it might be some work towards adding extensions, but it doesn't match the PR description as is.

analysis_options.yaml

lib/src/empty_unmodifiable_set.dart

lib/src/algorithms.dart

lrhn · 2020-05-14T07:16:49Z

Whoops. Forgot to git-add the new files.

lib/src/iterable_extensions.dart

natebosch · 2020-05-14T16:48:06Z

lib/src/list_extensions.dart

+  }
+
+  /// Maps each element and its index to a new value.
+  Iterable<R> mapIndexed<R>(R convert(int index, E element)) sync* {


How much value are we buying by specializing this against Iterable.mapIndexed? Do we expect this[index] to be meaningfully different (faster?) than for(var element in this)?

Faster, but possibly not by a lot.
It has a better chance of ending up monomorphic.

lib/src/list_extensions.dart

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mit-mit · 2020-09-17T13:44:09Z

@lrhn looks stale?

lrhn · 2020-09-17T14:00:43Z

Was waiting for null-safety. I should be able to continue this now.

googlebot · 2020-09-28T09:50:14Z

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lrhn · 2020-09-28T18:29:49Z

PTAL

natebosch · 2020-09-28T18:32:17Z

I had been waiting to review after the merge conflicts were resolved... Do you want me to do a first pass and then re-review after solving the conflicts?

lrhn · 2020-09-28T18:49:25Z

Conflicts should be gone now.

lib/src/algorithms.dart

lib/src/iterable_extensions.dart

natebosch

Overall I'm slightly worried about adding so many of these speculatively since there is a high cost to remove them, but given that they are extension methods I think the overall cost to keeping them is low.

CHANGELOG.md

test/extensions_test.dart

Add a number of useful extension methods to List and Iterable, and to a few other types. Also add a quick-sort implementation that these can extension methods can defer to, one which allows sorting only a range of the list.

lrhn

Addressed comments.

lib/src/iterable_extensions.dart

lrhn · 2020-09-28T09:02:58Z

lib/src/iterable_extensions.dart

+
+  /// The elements of this iterable with duplicates removed.
+  Iterable<T> unique() sync* {
+    var seen = <T>{};


Probably on the web, not on the VM.
On the other hand, most people use {}, so if this is the only code using HashSet, it will increase the compiled size of the web code. Dropping the method anyway.

lrhn · 2020-09-28T09:04:46Z

lib/src/iterable_extensions.dart

+    var result = <K, Set<T>>{};
+    for (var element in this) {
+      var key = keyOf(element);
+      result[key] = (result[key] ?? {})..add(element);


I don't think I was trying to optimize, just ended up here and didn't recognize it could be written even shorter.

lrhn · 2020-09-28T09:17:21Z

lib/src/iterable_extensions.dart

+  /// var parts = [1, 2, 3, 4, 5, 6, 7, 8, 9].split(isPrime);
+  /// print(parts); // ([1], [2], [3, 4], [5, 6], [7, 8, 9])
+  /// ```
+  Iterable<List<T>> splitBefore(bool test(T element)) =>


I've seen requests for something like it, for example https://stackoverflow.com/questions/22274033/how-do-i-split-or-chunk-a-list-into-equal-parts-with-dart

lrhn · 2020-09-28T09:19:05Z

lib/src/iterable_extensions.dart

+  /// The sum of the elements.
+  ///
+  /// The sum is zero if the iterable is empty.
+  T sum() {


I thought about it, and was on the fence about whether naming it for the operation or the result. If it's the operation, then it should be a method.
It's a little annoying that the best verb for the operation is also the best noun for the result. (Ditto for average. Truly, any noun can be verbed.)

Let's make them getters.

lib/src/iterable_extensions.dart

CHANGELOG.md

…#135) Add a number of useful extension methods to `List` and `Iterable`, and to a few other types. A good part of these extensions are backed by the algorithms of `algorithms.dart`, which is expanded to support them: * Added `quickSort`. * Add extra optional `Random` argument to `shuffle`. * Generalize some of the functions in algorithms.dart to work on specific properties of the objects (`binarySearchBy`, `lowerBoundBy`, `insertionSortBy`, `quickSortBy`, `mergeSortBy`). The new methods are not exported from the library yet, they are intended to be used through the extension.

googlebot added the cla: yes label May 13, 2020

lrhn requested a review from natebosch May 13, 2020 13:36

natebosch suggested changes May 13, 2020

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natebosch suggested changes May 14, 2020

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lrhn added cla: yes and removed cla: no labels Jun 15, 2020

lrhn mentioned this pull request Sep 17, 2020

Extensions null safety #139

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lrhn force-pushed the extensions branch from e88832c to c5bdddd Compare September 28, 2020 09:50

lrhn force-pushed the extensions branch from c5bdddd to 554721e Compare September 28, 2020 18:48

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lrhn added 2 commits September 30, 2020 11:49

Add extension methods to package:collection.

3f7627f

Add a number of useful extension methods to List and Iterable, and to a few other types. Also add a quick-sort implementation that these can extension methods can defer to, one which allows sorting only a range of the list.

Address comments

6064ea3

lrhn force-pushed the extensions branch from 69dd04f to 6064ea3 Compare September 30, 2020 09:55

lrhn commented Sep 30, 2020

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lrhn merged commit 7d44763 into master Sep 30, 2020

natebosch deleted the extensions branch September 30, 2020 16:49

lrhn mentioned this pull request May 27, 2021

Null safety feedback: How to use firstWhere? dart-lang/sdk#42947

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Add extension methods to package:collection. #135

Add extension methods to package:collection. #135

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Add extension methods to package:collection. #135

Add extension methods to package:collection. #135

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