Quiver is a set of utility libraries for Dart that makes using many Dart libraries easier and more convenient, or adds additional functionality.

API Docs are available.

Add Quiver to your project's pubspec.yaml file and run pub get. We recommend the following version constraint:

dependencies:
  quiver: '>=0.23.0<0.24.0'

Utilities for working with Futures, Streams and async computations.

collect collects the completion events of an Iterable of Futures into a Stream.

enumerate and concat represent Stream versions of the same-named quiver.iterables methods.

doWhileAsync, reduceAsync and forEachAsync perform async computations on the elements of on Iterables, waiting for the computation to complete before processing the next element.

StreamBuffer allows for the orderly reading of elements from a stream, such as a socket.

FutureGroup is collection of Futures that signals when all its child futures have completed. Allows adding new Futures as long as it hasn't completed yet. Useful when async tasks can spwn new async tasks and you need to wait for all of them to complete.

FutureStream turns a Future<Stream> into a Stream which emits the same events as the stream returned from the future.

StreamRouter splits a Stream into mulltiple streams based on a set of predicates.

CountdownTimer is a simple countdown timer that fires events in regular increments.

CreateTimer and CreateTimerPeriodic are typedefs that are useful for passing Timer factories to classes and functions, increasing the testability of code that depends on Timer.

Metronome is a self-correcting alternative to Timer.periodic. It provides a simple, tracking periodic stream of DateTime events with optional anchor time.

Cache is a semi-persistent, asynchronously accessed, mapping of keys to values. Caches are similar to Maps, except that the cache implementation might store values in a remote system, so all operations are asynchronous, and caches might have eviction policies.

MapCache is a Cache implementation backed by a Map.

checkArgument throws ArgumentError if the specifed argument check expression is false.

checkListIndex throws RangeError if the specified index is out of bounds.

checkNotNull throws ArgumentError if the specified argument is null.

checkState throws StateError if the specifed state check expression is false.

listsEqual, mapsEqual and setsEqual check collections for equality.

LruMap is a map that removes the least recently used item when a threshold length is exceeded.

Multimap is an associative collection that maps keys to collections of values.

BiMap is a bidirectional map and provides an inverse view, allowing lookup of key by value.

TreeSet is a balanced binary tree that offers a bidirectional iterator, the ability to iterate from an arbitrary anchor, and 'nearest' search.

Optional is a way to represent optional values without allowing null.

firstNonNull returns its first non-null argument.

hashObjects, hash2, hash3, and hash4 generate high-quality hashCodes for a list of objects, or 2, 3, or 4 arguments respectively.

visitDirectory is a recursive directory lister that conditionally recurses into sub-directories based on the result of a handler function.

concat, count, cycle, enumerate, merge, partition, range, and zip create, transform, or combine Iterables in different ways, similar to Python's itertools.

min, max, and extent retreive the minimum and maximum elements from an iterable.

GeneratingIterable is an easy way to create lazy iterables that produce elements by calling a function. A common use-case is to traverse properties in an object graph, like the parent relationship in a tree.

InfiniteIterable is a base class for Iterables that throws on operations that require a finite length.

getTypeName returns the name of a Type instance.

implements and classImplements determine if an instance or ClassMirror, respectively, implement the interface represented by a Type instance. They implement the behavior of is for mirrors, except for generics.

getMemberMirror searches though a ClassMirror and its class hierarchy for a member. This makes up for the fact that ClassMirror.members doesn't contain members from interfaces or superclasses.

Method wraps an InstanceMirror and Symbol to create a callable that invokes a method on the instance. It in effect closurizes a method reflectively.

pattern.dart container utilities for work with Patterns and RegExps.

Glob implements glob patterns that are commonly used with filesystem paths.

matchesAny combines multiple Patterns into one, and allows for exclusions.

matchesFull returns true if a Pattern matches an entire String.

escapeRegex escapes special regex characters in a String so that it can be used as a literal match inside of a RegExp.

isBlank checks if a string is null, empty or made of whitespace characters.

isEmpty checks if a string is null or empty.

equalsIgnoreCase checks if two strings are equal, ignoring case.

compareIgnoreCase compares two strings, ignoring case.

flip flips the order of characters in a string.

nullToEmpty turns null to empty string, and returns non-empty strings unchanged.

emptyToNull turns empty string to null, and returns non-empty strings unchanged.

repeat concatenates a string to itself a given number of times.

loop allows you to loop through characters in a string starting and ending at arbitrary indices. Out of bounds indices allow you to wrap around the string, supporting a number of use-cases, including:

• Rotating: loop('lohel', -3, 2) => 'hello'
• Repeating, like repeat, but with better character-level control, e.g.: loop('la ', 0, 8) => 'la la la' // no tailing space
• Tailing: loop('/path/to/some/file.txt', -3) => 'txt'
• Reversing: loop('top', 3, 0) => 'pot'

Clock provides points in time relative to the current point in time, for example: now, 2 days ago, 4 weeks from now, etc. For tesability, use Clock rather than other ways of accessing time, like new DateTime(), so that you can use a fake time function in your tests to control time.

Now is a typedef for functions that return the current time in microseconds, since Clock deals in DateTime which only have millisecond accuracy.

aMicrosecond, aMillisecond, aSecond, aMinute, anHour, aDay, and aWeek are unit duration constants to allow writing for example:

• aDay vs. const Duration(days: 1)
• aSecond * 30 vs. const Duration(seconds: 30)

The Quiver testing libraries are intended to be used in testing code, not production code. It currently consists of fake implementations of some Quiver interfaces.

FakeAsync enables testing of units which depend upon timers and microtasks. It supports fake advancements of time and the microtask queue, which cause fake timers and microtasks to be processed. A Clock is provided from which to read the current fake time. Faking synchronous or blocking time advancement is also supported.

areEqualityGroups is a matcher that supports testing operator== and hashCode implementations.

assertCheckedMode asserts the current runtime has checked mode enabled.

FakeStopwatch is a Stopwatch that uses a provided now() function to get the current time.