collection 1.14.6

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Contains utility functions and classes in the style of dart:collection to make working with collections easier.


The package contains functions that operate on lists.

It contains ways to shuffle a List, do binary search on a sorted List, and various sorting algorithms.


The package provides a way to specify the equality of elements and collections.

Collections in Dart have no inherent equality. Two sets are not equal, even if they contain exactly the same objects as elements.

The Equality interface provides a way to say define such an equality. In this case, for example, const SetEquality(const IdentityEquality()) is an equality that considers two sets equal exactly if they contain identical elements.

Equalities are provided for Iterables, Lists, Sets, and Maps, as well as combinations of these, such as:

const MapEquality(const IdentityEquality(), const ListEquality());

This equality considers maps equal if they have identical keys, and the corresponding values are lists with equal (operator==) values.

Iterable Zip

Utilities for "zipping" a list of iterables into an iterable of lists.

Priority Queue

An interface and implementation of a priority queue.


The package contains classes that "wrap" a collection.

A wrapper class contains an object of the same type, and it forwards all methods to the wrapped object.

Wrapper classes can be used in various ways, for example to restrict the type of an object to that of a supertype, or to change the behavior of selected functions on an existing object.

Features and bugs

Please file feature requests and bugs at the issue tracker.


  • Make DefaultEquality's equals() and hash() methods take any Object rather than objects of type E. This makes const DefaultEquality<Null>() usable as Equality<E> for any E, which means it can be used in a const context which expects Equality<E>.

    This makes the default arguments of various other const equality constructors work in strong mode.


  • Fix issue with EmptyUnmodifiableSet's stubs that were introduced in 1.14.4.


  • Add implementation stubs of upcoming Dart 2.0 core library methods, namely new methods for classes that implement Iterable, List, Map, Queue, and Set.


  • Fix MapKeySet.lookup to be a valid override in strong mode.


  • Add type arguments to SyntheticInvocation.


  • Make Equality implementations accept null as argument to hash.


  • Add CombinedListView, a view of several lists concatenated together.
  • Add CombinedIterableView, a view of several iterables concatenated together.
  • Add CombinedMapView, a view of several maps concatenated together.


  • Add EqualityBy


  • Add CaseInsensitiveEquality.

  • Fix bug in equalsIgnoreAsciiCase.


  • Add EqualityMap and EqualitySet classes which use Equality objects for key and element equality, respectively.


  • Set.difference now takes a Set<Object> as argument.


  • Fix some documentation bugs.


  • Add a top-level stronglyConnectedComponents() function that returns the strongly connected components in a directed graph.


  • Add a top-level mapMap() function that works like on a Map.

  • Add a top-level mergeMaps() function that creates a new map with the combined contents of two existing maps.

  • Add a top-level groupBy() function that converts an Iterable to a Map by grouping its elements using a function.

  • Add top-level minBy() and maxBy() functions that return the minimum and maximum values in an Iterable, respectively, ordered by a derived value.

  • Add a top-level transitiveClosure() function that returns the transitive closure of a directed graph.


  • Add a const UnmodifiableSetView.empty() constructor.


  • Add a UnionSet class that provides a view of the union of a set of sets.

  • Add a UnionSetController class that provides a convenient way to manage the contents of a UnionSet.

  • Fix another incorrectly-declared generic type.


  • Fix an incorrectly-declared generic type.


  • Add DelegatingIterable.typed(), DelegatingList.typed(), DelegatingSet.typed(), DelegatingMap.typed(), and DelegatingQueue.typed() static methods. These wrap untyped instances of these classes with the correct type parameter, and assert the types of values as they're accessed.

  • Fix the types for binarySearch() and lowerBound() so they no longer require all arguments to be comparable.

  • Add generic annotations to insertionSort() and mergeSort().


  • Fix all strong mode warnings.


  • Add a new PriorityQueue() constructor that forwards to new HeapPriorityQueue().

  • Deprecate top-level libraries other than package:collection/collection.dart, which exports these libraries' interfaces.


  • Add lowerBound to binary search for values that might not be present.

  • Verify that the is valid for CanonicalMap.[].


  • Add string comparators that ignore ASCII case and sort numbers numerically.


  • Fix type inconsistencies with Map and Set.


  • Export UnmodifiableMapView from the Dart core libraries.


  • Bug-fix for signatures of isValidKey arguments of CanonicalizedMap.


  • Add a QueueList class that implements both Queue and List.


  • Add a CanonicalizedMap class that canonicalizes its keys to provide a custom equality relation.


  • Fix all analyzer hints.


  • Add a MapKeySet class that exposes an unmodifiable Set view of a Map's keys.

  • Add a MapValueSet class that takes a function from values to keys and uses it to expose a Set view of a Map's values.

Use this package as a library

1. Depend on it

Add this to your package's pubspec.yaml file:

  collection: ^1.14.6

2. Install it

You can install packages from the command line:

with pub:

$ pub get

Alternatively, your editor might support pub get. Check the docs for your editor to learn more.

3. Import it

Now in your Dart code, you can use:

import 'package:collection/collection.dart';
Version Uploaded Documentation Archive
1.14.11 Jul 18, 2018 Go to the documentation of collection 1.14.11 Download collection 1.14.11 archive
1.14.10 Jun 12, 2018 Go to the documentation of collection 1.14.10 Download collection 1.14.10 archive
1.14.9 Mar 20, 2018 Go to the documentation of collection 1.14.9 Download collection 1.14.9 archive
1.14.7 Mar 13, 2018 Go to the documentation of collection 1.14.7 Download collection 1.14.7 archive
1.14.6 Mar 6, 2018 Go to the documentation of collection 1.14.6 Download collection 1.14.6 archive
1.14.5 Jan 3, 2018 Go to the documentation of collection 1.14.5 Download collection 1.14.5 archive
1.14.4 Jan 3, 2018 Go to the documentation of collection 1.14.4 Download collection 1.14.4 archive
1.14.3 Jul 20, 2017 Go to the documentation of collection 1.14.3 Download collection 1.14.3 archive
1.14.2 Jul 7, 2017 Go to the documentation of collection 1.14.2 Download collection 1.14.2 archive
1.14.1 May 22, 2017 Go to the documentation of collection 1.14.1 Download collection 1.14.1 archive

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The package version is not analyzed, because it does not support Dart 2. Until this is resolved, the package will receive a health and maintenance score of 0.

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Package Constraint Resolved Available
Direct dependencies
Dart SDK >=1.21.0 <2.0.0