darq 1.1.1
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The power of lazy-evaluated enumerables in your hands! (A port of functional LINQ from the .NET library.)

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A port of .NET's LINQ IEnumerable functions to Dart. This package extends the native Iterable type with all of the LINQ methods that do not exist in native Dart. Starting with version 0.5, this package also contains the extension methods from the MoreLINQ .NET library.

API Reference #

Usage #

Because this library uses Dart 2.6's new extension methods, any Iterable has access to these methods as though they were native methods. This includes classes that extend from Iterable, such as List and Set.

In addition, this library adds several new types of Iterable classes to make some utility functions easier:

// Creates an iterable containing the numbers from 2 to 6: [2, 3, 4, 5, 6]
var rangeI = RangeIterable(2, 6, inclusive: true);

// Creates an iterable that contains 3 copies of the value 'abc': ['abc', 'abc', 'abc']
var repeatI = RepeatIterable('abc', 3);

// Creates an iterable from a string, iterating over its characters
// This is an extension getter property on String that returns an 
// iterable via `String.codeUnits.map((u) => String.fromCodeUnit(u))`.
// Results in ['a', 'b', 'c', 'd', 'e', 'f']
var stringI = 'abcdef'.iterable;

// Same as above but using `runes` instead of `codeUnits` to respect 
// rune boundaries and maintain surrogate pairs.
var stringIR = 'abcdef'.iterableRunes;

You can call any of 40 new methods on it to modify or analyze it. For example, the native method map is expanded upon with select, which combines the element with the index at which the element is found within the iterable:

var list = [10, 20, 30];
var mappedList = list.select((i, index) => '$index-$i'); // ['1-10', '2-20', '3-30']

There are "OrDefault" variants on several common iterator value getter methods, such as firstOrDefault, singleOrDefault, and defaultIfEmpty. Instead of throwing an error, these methods will return a default value (or null if left unspecified) if the element(s) cannot be found:

var list = <String>[];

var native = list.first; // Throws a StateError
var orDefault = list.firstOrDefault('abc'); // Returns 'abc'

var list2 = [1, 2, 3];
var importantValue = list2.where((i) => i >= 4)
                          .defaultIfEmpty(-1); // Returns [-1]

You can filter an iterable down to unique instances of elements with the distinct method:

var list = [1, 1, 1, 2, 2, 3, 4, 5, 5, 5, 5, 5];
var uniqueList = myEnum.distinct(); // [1, 2, 3, 4, 5]

There are also set operations with the except, intersect, and union methods:

var listA = [1, 2, 3, 4];
var listB = [3, 4, 5, 6];

var exclusion = listA.except(listB);       // [1, 2]
var intersection = listA.intersect(listB); // [3, 4]
var union = listA.union(listB);            // [1, 2, 3, 4, 5, 6]

And you can group elements together by common features using groupBy:

var list = [1, 2, 3, 4, 5, 6];
var groupedList = list.groupBy((i) => i / 3 == 0); // [[1, 2, 4, 5], [3, 6]]

Or bundle them into groups of a fixed length using segment:

var list = [1, 2, 3, 4, 5, 6];
var segmented = list.segment(2); // [[1, 2], [3, 4], [5, 6]]

You can even perform complex ordering functions using orderBy and thenBy:

var list = ['ab', 'a', 'c', 'aa', ''];
// Sort by string length followed by alphabetical order
var ordered = list.orderBy((c) => c.length)
                  .thenBy((c) => c);
// Result: ['', 'a', 'c', 'aa', 'ab']

Just like in native dart, every method returns a new Iterable, so you can chain methods together to make complex mapping, grouping, and filtering behavior:

var list = [3, 1, 6, 2, 3, 2, 4, 1];
var result = list.select((i, idx) => i * 2 + idx)     // [6, 3, 14, 8, 10, 10, 14, 9]
                 .distinct()                          // [6, 3, 14, 8, 10, 9]
                 .where((i) => i > 4)                 // [6, 14, 8, 10, 9]
                 .orderBy((i) => i)                   // [6, 8, 9, 10, 14]
                 .map((i) => i.toRadixString(16));    // [6, 8, 9, A, E]

Tuples #

As a necessity for some operations, I needed a Tuple class, and as I was unsatisfied with the current offerings out there right now, I elected to create my own.

For the uninitiated, tuples are similar to lists in concept that they contain multiple values addressable by index. But where every element of a list must resolve to the same type (the type of the list), each element in a tuple can be its own specified type. This results in being able to contain, distribute, and access the items in a tuple in a type-safe way. You could, for example, use a Tuple2<double, String> to return two values from a function and be able to access both the double and the String values without needing to resort to fragile methods such as dynamic or runtime type casting. Another difference between lists and tuples is that tuples are inherently immutable, so they aren't susceptible to side effects stemming from mutation and can even benefit from being declared as constants.

This package exposes tuple classes from Tuple0 up to Tuple9, depending on how many items the tuple contains. (Yes, I agree that Tuple0 and Tuple1 seem largely redundant, but I've seen them exist in the tuple libraries of many programming languages so it must serve some purpose or other, so I included them here all the same for completeness if nothing else.) Each tuple class includes the following features:

  • Constant constructors allow for efficient use of known tuple values.
  • Includes access to the item(s) by getter (tuple.item2) or by indexer(tuple[2]). (Note that access by indexer is not type-safe)
  • Factory constructor fromJson and method toJson means tuples are seralization-ready.
  • Additional factory constructor fromList to generate a tuple from a list (automatically casting when specifying type parameters for the constructor).
  • An asType method allows freely casting the tuple from any assortment of types to any other assortment of types (provided the items are compatible with those types).
    • Additionally, there is an asDynamic convenience method for casting a tuple to dynamic items.
  • Although tuples themselves are immutable, a copyWith method allows easy generation of duplicate tuples, optionally specifying new values for specific items.
    • Additionally, a copyWithout method allows selective filtering of items from a tuple resulting in a lower-order tuple.
  • A mapActions method allows you to iterate over each item with an exhaustive list of type-safe callbacks.
  • Each tuple class extends Iterable<dynamic>, so it can be treated as a normal iterable (and thus combined with any darq extension method).
  • As == and hashCode are both implemented, tuples can be directly compared for equality or used as keys for maps and other hash sets.

MoreLINQ Extension Methods #

As of version 0.5, this package also contains the extension methods from the MoreLINQ .NET library. This more than triples the available number of extension methods over vanilla LINQ.

Some examples of the new methods from MoreLINQ include:

index:

var list = ['a', 'b', 'c'];
var indexedList = list.index();

// Iterable:
// [ [0, 'a'], [1, 'b'], [2, 'c'] ]

assertAll:

var list = [2, 4, 5];
list.assertAll((x) => x.isEven);

// Throws an assertion error

awaitAll:

var list = [
  Future.delayed(Duration(seconds: 1)),
  Future.delayed(Duration(seconds: 2)),
  Future.delayed(Duration(seconds: 3)),
];
await list.awaitAll();

// Waits for 3 seconds before continuing

subsets:

var list = [1, 2, 3];
var subsets = list.subsets();

// Iterable: 
// [ [], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3] ]

interleave:

var listA = [1, 3, 5];
var listB = [2, 4, 6];
var combined = listA.interleave(listB);

// Iterable:
// [1, 2, 3, 4, 5, 6]

permutations:

var list = [1, 2, 3];
var perms = list.permutations();

// Iterable:
// [ [1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1] ]

split:

var list = ['a', ' ', 'b', 'c', ' ', 'd'];
var split = list.split(' ');

// Iterable:
// [ ['a'], ['b', 'c'], ['d'] ]

New Iterable Types #

String Extension Methods #

Iterable Extension Methods #

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The power of lazy-evaluated enumerables in your hands! (A port of functional LINQ from the .NET library.)

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andrew.ackie@gmail.com

License

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