Swift Standard Library: Documented and undocumented built-in functions in the 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, { $0 * 5 }), [5, 10, 15])
for i in map(1...10, { $0 * 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, { $0 * $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(...)

original article：Here