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[stdlib] Constrain Sequence methods that return AnySequence #12029

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Oct 3, 2017
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[stdlib] Constrain Sequence methods that return AnySequence #12029

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292 changes: 146 additions & 146 deletions stdlib/public/core/Sequence.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -331,7 +331,7 @@ public protocol Sequence {
associatedtype Iterator : IteratorProtocol where Iterator.Element == Element

/// A type that represents a subsequence of some of the sequence's elements.
associatedtype SubSequence : Sequence
associatedtype SubSequence : Sequence = AnySequence<Element>
where Element == SubSequence.Element,
SubSequence.SubSequence == SubSequence

Expand Down Expand Up @@ -879,149 +879,6 @@ extension Sequence {
return Array(result)
}

/// Returns a subsequence, up to the given maximum length, containing the
/// final elements of the sequence.
///
/// The sequence must be finite. If the maximum length exceeds the number of
/// elements in the sequence, the result contains all the elements in the
/// sequence.
///
/// let numbers = [1, 2, 3, 4, 5]
/// print(numbers.suffix(2))
/// // Prints "[4, 5]"
/// print(numbers.suffix(10))
/// // Prints "[1, 2, 3, 4, 5]"
///
/// - Parameter maxLength: The maximum number of elements to return. The
/// value of `maxLength` must be greater than or equal to zero.
/// - Complexity: O(*n*), where *n* is the length of the sequence.
@_inlineable
public func suffix(_ maxLength: Int) -> AnySequence<Element> {
_precondition(maxLength >= 0, "Can't take a suffix of negative length from a sequence")
if maxLength == 0 { return AnySequence([]) }
// FIXME: <rdar://problem/21885650> Create reusable RingBuffer<T>
// Put incoming elements into a ring buffer to save space. Once all
// elements are consumed, reorder the ring buffer into an `Array`
// and return it. This saves memory for sequences particularly longer
// than `maxLength`.
var ringBuffer: [Element] = []
ringBuffer.reserveCapacity(Swift.min(maxLength, underestimatedCount))

var i = ringBuffer.startIndex

for element in self {
if ringBuffer.count < maxLength {
ringBuffer.append(element)
} else {
ringBuffer[i] = element
i += 1
i %= maxLength
}
}

if i != ringBuffer.startIndex {
let s0 = ringBuffer[i..<ringBuffer.endIndex]
let s1 = ringBuffer[0..<i]
return AnySequence([s0, s1].joined())
}
return AnySequence(ringBuffer)
}

/// Returns the longest possible subsequences of the sequence, in order, that
/// don't contain elements satisfying the given predicate. Elements that are
/// used to split the sequence are not returned as part of any subsequence.
///
/// The following examples show the effects of the `maxSplits` and
/// `omittingEmptySubsequences` parameters when splitting a string using a
/// closure that matches spaces. The first use of `split` returns each word
/// that was originally separated by one or more spaces.
///
/// let line = "BLANCHE: I don't want realism. I want magic!"
/// print(line.split(whereSeparator: { $0 == " " })
/// .map(String.init))
/// // Prints "["BLANCHE:", "I", "don\'t", "want", "realism.", "I", "want", "magic!"]"
///
/// The second example passes `1` for the `maxSplits` parameter, so the
/// original string is split just once, into two new strings.
///
/// print(
/// line.split(maxSplits: 1, whereSeparator: { $0 == " " })
/// .map(String.init))
/// // Prints "["BLANCHE:", " I don\'t want realism. I want magic!"]"
///
/// The final example passes `true` for the `allowEmptySlices` parameter, so
/// the returned array contains empty strings where spaces were repeated.
///
/// print(
/// line.split(
/// omittingEmptySubsequences: false,
/// whereSeparator: { $0 == " " }
/// ).map(String.init))
/// // Prints "["BLANCHE:", "", "", "I", "don\'t", "want", "realism.", "I", "want", "magic!"]"
///
/// - Parameters:
/// - maxSplits: The maximum number of times to split the sequence, or one
/// less than the number of subsequences to return. If `maxSplits + 1`
/// subsequences are returned, the last one is a suffix of the original
/// sequence containing the remaining elements. `maxSplits` must be
/// greater than or equal to zero. The default value is `Int.max`.
/// - omittingEmptySubsequences: If `false`, an empty subsequence is
/// returned in the result for each pair of consecutive elements
/// satisfying the `isSeparator` predicate and for each element at the
/// start or end of the sequence satisfying the `isSeparator` predicate.
/// If `true`, only nonempty subsequences are returned. The default
/// value is `true`.
/// - isSeparator: A closure that returns `true` if its argument should be
/// used to split the sequence; otherwise, `false`.
/// - Returns: An array of subsequences, split from this sequence's elements.
@_inlineable
public func split(
maxSplits: Int = Int.max,
omittingEmptySubsequences: Bool = true,
whereSeparator isSeparator: (Element) throws -> Bool
) rethrows -> [AnySequence<Element>] {
_precondition(maxSplits >= 0, "Must take zero or more splits")
var result: [AnySequence<Element>] = []
var subSequence: [Element] = []

@discardableResult
func appendSubsequence() -> Bool {
if subSequence.isEmpty && omittingEmptySubsequences {
return false
}
result.append(AnySequence(subSequence))
subSequence = []
return true
}

if maxSplits == 0 {
// We aren't really splitting the sequence. Convert `self` into an
// `Array` using a fast entry point.
subSequence = Array(self)
appendSubsequence()
return result
}

var iterator = self.makeIterator()
while let element = iterator.next() {
if try isSeparator(element) {
if !appendSubsequence() {
continue
}
if result.count == maxSplits {
break
}
} else {
subSequence.append(element)
}
}
while let element = iterator.next() {
subSequence.append(element)
}
appendSubsequence()
return result
}

/// Returns a value less than or equal to the number of elements in
/// the sequence, nondestructively.
///
Expand Down Expand Up @@ -1176,15 +1033,158 @@ extension Sequence where Element : Equatable {
separator: Element,
maxSplits: Int = Int.max,
omittingEmptySubsequences: Bool = true
) -> [AnySequence<Element>] {
) -> [SubSequence] {
return split(
maxSplits: maxSplits,
omittingEmptySubsequences: omittingEmptySubsequences,
whereSeparator: { $0 == separator })
}
}

extension Sequence {
extension Sequence where SubSequence == AnySequence<Element> {

/// Returns the longest possible subsequences of the sequence, in order, that
/// don't contain elements satisfying the given predicate. Elements that are
/// used to split the sequence are not returned as part of any subsequence.
///
/// The following examples show the effects of the `maxSplits` and
/// `omittingEmptySubsequences` parameters when splitting a string using a
/// closure that matches spaces. The first use of `split` returns each word
/// that was originally separated by one or more spaces.
///
/// let line = "BLANCHE: I don't want realism. I want magic!"
/// print(line.split(whereSeparator: { $0 == " " })
/// .map(String.init))
/// // Prints "["BLANCHE:", "I", "don\'t", "want", "realism.", "I", "want", "magic!"]"
///
/// The second example passes `1` for the `maxSplits` parameter, so the
/// original string is split just once, into two new strings.
///
/// print(
/// line.split(maxSplits: 1, whereSeparator: { $0 == " " })
/// .map(String.init))
/// // Prints "["BLANCHE:", " I don\'t want realism. I want magic!"]"
///
/// The final example passes `true` for the `allowEmptySlices` parameter, so
/// the returned array contains empty strings where spaces were repeated.
///
/// print(
/// line.split(
/// omittingEmptySubsequences: false,
/// whereSeparator: { $0 == " " }
/// ).map(String.init))
/// // Prints "["BLANCHE:", "", "", "I", "don\'t", "want", "realism.", "I", "want", "magic!"]"
///
/// - Parameters:
/// - maxSplits: The maximum number of times to split the sequence, or one
/// less than the number of subsequences to return. If `maxSplits + 1`
/// subsequences are returned, the last one is a suffix of the original
/// sequence containing the remaining elements. `maxSplits` must be
/// greater than or equal to zero. The default value is `Int.max`.
/// - omittingEmptySubsequences: If `false`, an empty subsequence is
/// returned in the result for each pair of consecutive elements
/// satisfying the `isSeparator` predicate and for each element at the
/// start or end of the sequence satisfying the `isSeparator` predicate.
/// If `true`, only nonempty subsequences are returned. The default
/// value is `true`.
/// - isSeparator: A closure that returns `true` if its argument should be
/// used to split the sequence; otherwise, `false`.
/// - Returns: An array of subsequences, split from this sequence's elements.
@_inlineable
public func split(
maxSplits: Int = Int.max,
omittingEmptySubsequences: Bool = true,
whereSeparator isSeparator: (Element) throws -> Bool
) rethrows -> [AnySequence<Element>] {
_precondition(maxSplits >= 0, "Must take zero or more splits")
var result: [AnySequence<Element>] = []
var subSequence: [Element] = []

@discardableResult
func appendSubsequence() -> Bool {
if subSequence.isEmpty && omittingEmptySubsequences {
return false
}
result.append(AnySequence(subSequence))
subSequence = []
return true
}

if maxSplits == 0 {
// We aren't really splitting the sequence. Convert `self` into an
// `Array` using a fast entry point.
subSequence = Array(self)
appendSubsequence()
return result
}

var iterator = self.makeIterator()
while let element = iterator.next() {
if try isSeparator(element) {
if !appendSubsequence() {
continue
}
if result.count == maxSplits {
break
}
} else {
subSequence.append(element)
}
}
while let element = iterator.next() {
subSequence.append(element)
}
appendSubsequence()
return result
}

/// Returns a subsequence, up to the given maximum length, containing the
/// final elements of the sequence.
///
/// The sequence must be finite. If the maximum length exceeds the number of
/// elements in the sequence, the result contains all the elements in the
/// sequence.
///
/// let numbers = [1, 2, 3, 4, 5]
/// print(numbers.suffix(2))
/// // Prints "[4, 5]"
/// print(numbers.suffix(10))
/// // Prints "[1, 2, 3, 4, 5]"
///
/// - Parameter maxLength: The maximum number of elements to return. The
/// value of `maxLength` must be greater than or equal to zero.
/// - Complexity: O(*n*), where *n* is the length of the sequence.
@_inlineable
public func suffix(_ maxLength: Int) -> AnySequence<Element> {
_precondition(maxLength >= 0, "Can't take a suffix of negative length from a sequence")
if maxLength == 0 { return AnySequence([]) }
// FIXME: <rdar://problem/21885650> Create reusable RingBuffer<T>
// Put incoming elements into a ring buffer to save space. Once all
// elements are consumed, reorder the ring buffer into an `Array`
// and return it. This saves memory for sequences particularly longer
// than `maxLength`.
var ringBuffer: [Element] = []
ringBuffer.reserveCapacity(Swift.min(maxLength, underestimatedCount))

var i = ringBuffer.startIndex

for element in self {
if ringBuffer.count < maxLength {
ringBuffer.append(element)
} else {
ringBuffer[i] = element
i += 1
i %= maxLength
}
}

if i != ringBuffer.startIndex {
let s0 = ringBuffer[i..<ringBuffer.endIndex]
let s1 = ringBuffer[0..<i]
return AnySequence([s0, s1].joined())
}
return AnySequence(ringBuffer)
}

/// Returns a subsequence containing all but the given number of initial
/// elements.
Expand Down
2 changes: 0 additions & 2 deletions test/IDE/complete_from_stdlib.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -170,8 +170,6 @@ func testArchetypeReplacement3 (_ a : [Int]) {
// PRIVATE_NOMINAL_MEMBERS_7-DAG: Decl[InstanceVar]/Super: first[#Int?#]
// PRIVATE_NOMINAL_MEMBERS_7-DAG: Decl[InstanceMethod]/Super: map({#(transform): (Int) throws -> T##(Int) throws -> T#})[' rethrows'][#[T]#]
// PRIVATE_NOMINAL_MEMBERS_7-DAG: Decl[InstanceMethod]/Super: dropLast({#(n): Int#})[#ArraySlice<Int>#]
// PRIVATE_NOMINAL_MEMBERS_7-DAG: Decl[InstanceMethod]/Super: dropFirst({#(n): Int#})[#AnySequence<Int>#]
// PRIVATE_NOMINAL_MEMBERS_7-DAG: Decl[InstanceMethod]/Super: prefix({#(maxLength): Int#})[#AnySequence<Int>#]
// PRIVATE_NOMINAL_MEMBERS_7-DAG: Decl[InstanceMethod]/Super: elementsEqual({#(other): Sequence#}, {#by: (Int, Int) throws -> Bool##(Int, Int) throws -> Bool#})[' rethrows'][#Bool#]


Expand Down