LINQ for Swift - Swift Integrated Query
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README.md

SINQ - Swift Integrated Query

Swift has generic Collections and Sequences as well as some universal free functions to work with them. What is missing is a fluent interface that would make working with them easy¹ - like list comprehensions in many languages or LINQ in .NET. The operations should: require no typecasts, be easily chained, work on any sequences, be performed lazily where possible.

Overview

SINQ (or LINQ for Swift) is a Swift library for working with sequences / collections. It is, as name suggests, modelled after LINQ, but it is not necessarily intended to be a LINQ port. The library is still under development, just as Swift is. Any contributions, both in terms of suggestions/ideas or actual code are welcome.

SINQ is brought to you by Leszek Ślażyński (slazyk), you can follow me on twitter and github. Be sure to check out Observable-Swift my other library that implements value observing and events.

Examples

The main goal of SINQ is to provide a fluent interface for working with collections. The way it tries to accomplish that is with chaining of methods. Most of the operations are performed lazily, i.e. computations are deferred and done only for the part of the result you enumerate. Everything is typed - no typecasts required. Examples:

let nums1 = from([1, 4, 2, 3, 5]).whereTrue{ $0 > 2 }.orderBy{ $0 }.select{ 2 * $0 }
// or less (linq | sql)-esque 
let nums2 = sinq([1, 4, 2, 3, 5]).filter{ $0 > 2 }.orderBy{ $0 }.map{ 2 * $0 }

// path1 : String = ..., path2: String = ...
let commonComponents = sinq(path1.pathComponents)
    .zip(path2.pathComponents) { ($0, $1) }
    .takeWhile { $0 == $1 }
    .count()

let prefixLength = sinq(path1).zip(path2){ ($0, $1) }.takeWhile{ $0 == $1 }.count()

// available : String[] = ..., blacklist : String[] = ...
let next = sinq(available).except(blacklist){ $0 }.firstOrDefault("unknown")

// employees : Employee[] = ...

let headCnt = sinq(employees).groupBy{ $0.manager }.map{ ($0.key, $0.values.count()) }

let allTasks = from(employees).selectMany{ $0.tasks }.orderBy{ $0.priority }

let elite1 = sinq(employees).whereTrue{ $0.salary > 1337 }.orderBy{ $0.salary }
let elite2 = from(employees).orderBy{ $0.salary }.takeWhile{ $0.salary > 1337 }

// products : Product[] = ..., categories : Category[] = ...

let breadcrumbs = sinq(categories).join(inner: products,
                                     outerKey: { $0.id },
                                     innerKey: { $0.categoryId },
                                       result: { "\($0.name) / \($1.name)" })

Please note that the results are not cached, i.e. looping twice over result of orderBy(...) will perform two sorts. If you want to use results multiple times, you can get always array with toArray().

It uses SinqSequence<T> wrapper struct in order to do that, you can wrap any Sequence by simply sinq(seq), from(seq), or SinqSequence(seq). This wrapper is introduced because Swift does not allow for adding methods to protocols (like Sequence) and because extending existing SequenceOf<T> causes linker errors.

While I do try to follow cocoa-like naming and spelling conventions, while also keeping the LINQ naming where reasonable, I refuse to call the struct SINQSequence<T> or SSequence<T>.

Installation

You can use either CocoaPods or Carthage to install SINQ.

Otherwise, the easiest option to use SINQ in your project is to clone this repo and add SINQ.xcodeproj to your project/workspace and then add SINQ.framework to frameworks for your target.

After that you just import SINQ.

List of methods

aggregate / reduce - combine all the elements of the sequence into a result
aggregate(combine: (T, T) -> T) -> T
aggregate<R>(initial: R, combine: (R, T) -> R) -> R
aggregate<C, R>(initial: C, combine: (C, T) -> C, result: C -> R) -> R
all - check if a predicate is true for all the elements
all(predicate: T -> Bool) -> Bool
any - check if not empty, or if a predicate is true for any object
any() -> Bool      
any(predicate: T -> Bool) -> Bool
concat - create a sequence concatenating two sequences
concat<S: Sequence>(other: S) -> SinqSequence<T>
contains - check if the sequence contains an element
contains(value: T, equality: (T, T) -> Bool) -> Bool
contains<K: Equatable>(value: T, key: T -> K) -> Bool
count - count the elements in the sequence
func count() -> Int
distinct - create a sequence with unique elements, in order
distinct(equality: (T, T) -> Bool) -> SinqSequence<T>
distinct<K: Hashable>(key: T -> K) -> SinqSequence<T>
each - iterate over the sequence
each(function: T -> ()) -> ()  
elementAt - get element at given index from the sequence
elementAtOrNil(index: Int) -> T?  
elementAt(index: Int) -> T
elementAt(index: Int, orDefault: T) -> T
except - create sequence with unique elements, excluding given
except<S: Sequence>(sequence: S, equality: (T, T) -> Bool) -> SinqSequence<T> 
except<S: Sequence, K: Hashable>(sequence: S, key: T -> K) -> SinqSequence<T>  
first - get first element of the sequence [satisfying a predicate]
first() -> T
firstOrNil() -> T?
first(predicate: T -> Bool) -> T
firstOrDefault(defaultElement: T) -> T
firstOrNil(predicate: T -> Bool) -> T?
firstOrDefault(defaultElement: T, predicate: T -> Bool) -> T
groupBy - create a sequence grouping elements by given key
groupBy<K: Hashable>(key: T -> K) -> SinqSequence<Grouping<K, T>>
groupBy<K: Hashable, V>(key: T -> K, element: T -> V) -> SinqSequence<Grouping<K, V>>
groupBy<K: Hashable, V, R>(key: T -> K, element: T -> V, result: (K, SinqSequence<V>) -> R) -> SinqSequence<R>
groupJoin - create a sequence joining two sequences with grouping
groupJoin<S: Sequence, K: Hashable>
	(#inner: S, outerKey: T -> K, innerKey: S.E -> K)
	-> SinqSequence<Grouping<T, S.E>>
groupJoin<S: Sequence, K: Hashable, R>
	(#inner: S, outerKey: T -> K, innerKey: S.E -> K,
 	 result: (T, SinqSequence<S.E>) -> R) -> SinqSequence<R>
intersect - create a sequence with unique elements present in both sequences
intersect<S: Sequence>(sequence: S, equality: (T, T) -> Bool) -> SinqSequence<T>
intersect<S: Sequence, K: Hashable>(sequence: S, key: T -> K) -> SinqSequence<T>
join - create a sequence joining two sequences without grouping
join<S: Sequence, K: Hashable, R>
	(#inner: S, outerKey: T -> K, innerKey: S.E -> K,
     result: (T, S.E) -> R) -> SinqSequence<R>
join<S: Sequence, K: Hashable>
    (#inner: S, outerKey: T -> K, innerKey: S.E -> K)
    -> SinqSequence<(T, S.E)>
last - return last element in the sequence [satisfying a predicate]
last() -> T
lastOrNil() -> T?
last(predicate: T -> Bool) -> T
lastOrNil(predicate: T -> Bool) -> T?
lastOrDefault(defaultElement: T) -> T
lastOrDefault(defaultElement: T, predicate: T -> Bool) -> T
min / max - return the minimum/maximum value of a function for the sequence
min<R: Comparable>(key: T -> R) -> R
max<R: Comparable>(key: T -> R) -> R
argmin / argmax - return the element for which the function has the minimum/maximum value
argmin<R: Comparable>(key: T -> R) -> T
argmax<R: Comparable>(key: T -> R) -> T
orderBy / orderByDescending - create a sequence sorted by given key
orderBy<K: Comparable>(key: T -> K) -> SinqOrderedSequence<T>
orderByDescending<K: Comparable>(key: T -> K) -> SinqOrderedSequence<T>
reverse - create a sequence with reverse order
reverse() -> SinqSequence<T>
select / map - create a sequence with results of applying given function
select<V>(selector: T -> V) -> SinqSequence<V>
select<V>(selector: (T, Int) -> V) -> SinqSequence<V>
selectMany - create a sequence by concatenating function results for each element
selectMany<S: Sequence>(selector: T -> S) -> SinqSequence<S.E>
selectMany<S: Sequence>(selector: (T, Int) -> S) -> SinqSequence<S.E>
selectMany<S: Sequence, R>(selector: T -> S, result: S.E -> R) -> SinqSequence<R>
selectMany<S: Sequence, R>(selector: (T, Int) -> S, result: S.E -> R) -> SinqSequence<R>
single - return the only element in a sequence containing exactly one element
single() -> T
singleOrNil() -> T?
singleOrDefault(defaultElement: T) -> T
single(predicate: T -> Bool) -> T
singleOrNil(predicate: T -> Bool) -> T?
singleOrDefault(defaultElement: T, predicate: T -> Bool) -> T
skip - create a sequence skipping (given number of elements | while predicate holds )
skip(count: Int) -> SinqSequence<T>
skipWhile(predicate: T -> Bool) -> SinqSequence<T>
take - create a sequence by taking (given number of elements | while predicate holds )
take(count: Int) -> SinqSequence<T>
takeWhile(predicate: T -> Bool) -> SinqSequence<T>
thenBy / thenByDescending - create a sequence by additionally sorting on given key
thenBy<K: Comparable>(key: T -> K) -> SinqOrderedSequence<T>
thenByDescending<K: Comparable>(key: T -> K) -> SinqOrderedSequence<T>
toArray - create an array from the sequence
toArray() -> T[]
toDictionary / toLookupDictionary - create a dictionary from the sequence
toDictionary<K: Hashable, V>(keyValue: T -> (K, V)) -> Dictionary<K, V>
toDictionary<K: Hashable, V>(key: T -> K, value: T -> V) -> Dictionary<K, V>
toDictionary<K: Hashable>(key: T -> K) -> Dictionary<K, T>
union - create a sequence with unique elements from either of the sequences
union<S: Sequence>(sequence: S, equality: (T, T) -> Bool) -> SinqSequence<T>
union<S: Sequence, K: Hashable>(sequence: S, key: T -> K) -> SinqSequence<T>
whereTrue / filter - create a sequence only with elements satisfying a predicate
whereTrue(predicate: T -> Bool) -> SinqSequence<T>
zip - create a sequence by combining pairs of elements from two sequences
zip<S: Sequence, R>(sequence: S, result: (T, S.E) -> R) -> SinqSequence<R>

Troubleshooting

Due to bug in swift it sometimes happens that swift compiler and/or SourceKitService loop indefinitely while solving type constraints during compilation or indexing. If this happens, to help them solve the constraints, one might have to divide work for them into smaller pieces. For example this would cause inifinite loop:

func testAll() {
  XCTAssertTrue(sinq([11, 12, 15, 10]).all{ $0 >= 10 })
  XCTAssertFalse(sinq([11, 12, 15, 10]).all{ $0 > 10 })
}

While this does not:

func testAll() {
  let seq = sinq([11, 12, 15, 10])
  XCTAssertTrue(seq.all{ $0 >= 10 })
  XCTAssertFalse(seq.all{ $0 < 13 })
}

In this case it seems o be connected to @auto_closure arguments of XCTAssert*...

In case it happens for you, try to divide the statements like this or be more explicit in code about types and not depend as much on type inference.


¹ - this statement might become less true in the future, e.g. in Beta 4 Apple introduced lazy() which is similar to subset of sinq() in that it adds lazy chainable .map .filter .reverse .array and subscripting.