Swift Standard Library

Swift has 74 built-in functions but only seven of them are documented in the Swift book (“The Swift Programming Language”). The rest remain undocumented.

This article lists all built-in Swift functions – both documented and undocumented ones. The definition used for “built-in function” used in this article is a function available in Swift withoutimporting any modules (such as Foundation, etc.) or referencing any classes.

Let’s start with the seven documented built-in functions mentioned in the Swift book along with the page number on which the function was first mentioned:

 // assert mentioned on page 55
 assert(true)
 // countElements mentioned on page 79
 countElements("foo") == 3
 // enumerate mentioned on page 94
 for (i, j) in enumerate(["A", "B"]) {
     // "0:A", "1:B" will be printed
     println("\(i):\(j)")
 }
 // min mentioned on page 246
 min(8, 2, 3) == 2
 // print mentioned on page 85
 print("Hello ")
 // println mentioned on page 4
 println("World")
 // sort mentioned on page 14
 for i in sort(["B", "A"]) {
     // "A", "B" will be printed
     println(i)
 }

Now on to the most useful undocumented functions …

abs(signedNumber): Returns the absolute value of a given signed number. Trivial but not documented.

 abs(-1) == 1
 abs(-42) == 42
 abs(42) == 42

contains(sequence, element) : Returns true if a given sequence (such as an array) contains the specified element.

 var languages = ["Swift", "Objective-C"]
 contains(languages, "Swift") == true
 contains(languages, "Java") == false
 contains([29, 85, 42, 96, 75], 42) == true

dropFirst(sequence) : Returns a new sequence (such as an array) without the first element of the sequence.

 var languages = ["Swift", "Objective-C"]
 var oldLanguages = dropFirst(languages)
 equal(oldLanguages, ["Objective-C"]) == true

dropLast(sequence) : Returns a new sequence (such as an array) without the last element of the sequence passed as argument to the function.

 var languages = ["Swift", "Objective-C"]
 var newLanguages = dropLast(languages)
 equal(newLanguages, ["Swift"]) == true

dump(object): Dumps the contents of an object to standard output.

 var languages = ["Swift", "Objective-C"]
 dump(languages)
 // Prints:
 // ▿ 2 elements
 //   - [0]: Swift
 //   - [1]: Objective-C

equal(sequence1, sequence2): Returns true if sequence1 and sequence2 contain the same elements.

 var languages = ["Swift", "Objective-C"]
 equal(languages, ["Swift", "Objective-C"]) == true
 var oldLanguages = dropFirst(languages)
 equal(oldLanguages, ["Objective-C"]) == true

filter(sequence, includeElementClosure) : Returns a the elements from sequence that evaluate to true by includeElementClosure.

 for i in filter(1...100, { $0 % 10 == 0 }) {
     // 10, 20, 30, ...
     println(i)
     assert(contains([10, 20, 30, 40, 50, 60, 70, 80, 90, 100], i))
 }

find(sequence, element) : Return the index of a specified element in the given sequence. Or nil if the element is not found in the sequence.

 var languages = ["Swift", "Objective-C"]
 find(languages, "Objective-C") == 1
 find(languages, "Java") == nil
 find([29, 85, 42, 96, 75], 42) == 2

indices(sequence) : Returns the indices (zero indexed) of the elements in the given sequence.

 equal(indices([29, 85, 42]), [0, 1, 2])
 for i in indices([29, 85, 42]) {
     // 0, 1, 2
     println(i)
 }

join(separator, sequence) : Returns the elements of the supplied sequence separated by the given separator.

 join(":", ["A", "B", "C"]) == "A:B:C"
 var languages = ["Swift", "Objective-C"]
 join("/", languages) == "Swift/Objective-C"

map(sequence, transformClosure): Returns a new sequence with the transformClosure applied to all elements in the supplied sequence.

 equal(map(1...3, { $00 * 5 }), [5, 10, 15])
 for i in map(1...10, { $00 * 10 }) {
     // 10, 20, 30, ...
     println(i)
     assert(contains([10, 20, 30, 40, 50, 60, 70, 80, 90, 100], i))
 }

max(comparable1, comparable2, etc.): Returns the largest of the arguments given to the function.

 max(0, 1) == 1
 max(8, 2, 3) == 8

maxElement(sequence): Returns the largest element in a supplied sequence of comparable elements.

 maxElement(1...10) == 10
 var languages = ["Swift", "Objective-C"]
 maxElement(languages) == "Swift"

minElements(sequence) : Returns the smallest element in a supplied sequence of comparable elements.

 minElement(1...10) == 1
 var languages = ["Swift", "Objective-C"]
 minElement(languages) == "Objective-C"

reduce(sequence, initial, combineClosure): Recursively reduce the elements in sequence into one value by running the combineClosure on them with starting value of initial.

 var languages = ["Swift", "Objective-C"]
 reduce(languages, "", { $0 + $1 }) == "SwiftObjective-C"
 reduce([10, 20, 5], 1, { $00 * $1 }) == 1000

reverse(sequence): Returns the elements of the given sequence reversed.

 equal(reverse([1, 2, 3]), [3, 2, 1])
 for i in reverse([1, 2, 3]) {
     // 3, 2, 1
     println(i)
 }

startsWith(sequence1, sequence2): Return true if the starting elements sequence1 are equal to the of sequence2.

 startsWith("foobar", "foo") == true
 startsWith(10..100, 10..15) == true
 var languages = ["Swift", "Objective-C"]
 startsWith(languages, ["Swift"]) == true

Below is the full list of all 74 built-in functions in Swift. The functions covered above are the ones I think are useful on a day-to-day basis, but perhaps I’ve missed some functions from the list below that deserves coverage. If so, let me know in the comments section and please include a short code snippet to show how to use the function.

Happy Swifting!

 abs(...)
 advance(...)
 alignof(...)
 alignofValue(...)
 assert(...)
 bridgeFromObjectiveC(...)
 bridgeFromObjectiveCUnconditional(...)
 bridgeToObjectiveC(...)
 bridgeToObjectiveCUnconditional(...)
 c_malloc_size(...)
 c_memcpy(...)
 c_putchar(...)
 contains(...)
 count(...)
 countElements(...)
 countLeadingZeros(...)
 debugPrint(...)
 debugPrintln(...)
 distance(...)
 dropFirst(...)
 dropLast(...)
 dump(...)
 encodeBitsAsWords(...)
 enumerate(...)
 equal(...)
 filter(...)
 find(...)
 getBridgedObjectiveCType(...)
 getVaList(...)
 indices(...)
 insertionSort(...)
 isBridgedToObjectiveC(...)
 isBridgedVerbatimToObjectiveC(...)
 isUniquelyReferenced(...)
 join(...)
 lexicographicalCompare(...)
 map(...)
 max(...)
 maxElement(...)
 min(...)
 minElement(...)
 numericCast(...)
 partition(...)
 posix_read(...)
 posix_write(...)
 print(...)
 println(...)
 quickSort(...)
 reduce(...)
 reflect(...)
 reinterpretCast(...)
 reverse(...)
 roundUpToAlignment(...)
 sizeof(...)
 sizeofValue(...)
 sort(...)
 split(...)
 startsWith(...)
 strideof(...)
 strideofValue(...)
 swap(...)
 swift_MagicMirrorData_summaryImpl(...)
 swift_bufferAllocate(...)
 swift_keepAlive(...)
 toString(...)
 transcode(...)
 underestimateCount(...)
 unsafeReflect(...)
 withExtendedLifetime(...)
 withObjectAtPlusZero(...)
 withUnsafePointer(...)
 withUnsafePointerToObject(...)
 withUnsafePointers(...)
 withVaList(...)