Revert "Revert count(where:)"

benchmark/CMakeLists.txt

@@ -64,6 +64,7 @@ set(SWIFT_BENCH_MODULES
     single-source/ClassArrayGetter
     single-source/CodableTest
     single-source/Combos
+    single-source/CountAlgo
     single-source/DataBenchmarks
     single-source/DeadArray
     single-source/DevirtualizeProtocolComposition

benchmark/single-source/CountAlgo.swift

@@ -0,0 +1,127 @@
+//===--- CountAlgo.swift --------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+import TestsUtils
+
+public let CountAlgo = [
+  BenchmarkInfo(
+    name: "CountAlgoArray",
+    runFunction: run_CountAlgoArray,
+    tags: [.validation, .api]),
+  BenchmarkInfo(
+    name: "CountAlgoString",
+    runFunction: run_CountAlgoString,
+    tags: [.validation, .api],
+    legacyFactor: 5),
+]
+
+@inline(never)
+public func run_CountAlgoArray(_ N: Int) {
+  for _ in 1...10*N {
+    CheckResults(numbers.count(where: { $0 & 4095 == 0 }) == 25)
+  }
+}
+
+@inline(never)
+public func run_CountAlgoString(_ N: Int) {
+  let vowels = Set("aeiou")
+  for _ in 1...N {
+    CheckResults(text.count(where: vowels.contains) == 2014)
+  }
+}
+
+let numbers = Array(0..<100_000)
+
+let text = """
+    Lorem ipsum dolor sit amet, consectetur adipiscing elit. Maecenas tempus
+    dictum tellus placerat ultrices. Proin mauris risus, eleifend a elit ut,
+    semper consectetur nibh. Nulla ultricies est a vehicula rhoncus. Morbi
+    sollicitudin efficitur est a hendrerit. Interdum et malesuada fames ac ante
+    ipsum primis in faucibus. Lorem ipsum dolor sit amet, consectetur
+    adipiscing elit. Nulla facilisi. Sed euismod sagittis laoreet. Ut elementum
+    tempus ultrices. Donec convallis mauris at faucibus maximus.
+    Nullam in nunc sit amet ante tristique elementum quis ut eros. Fusce
+    dignissim, ante at efficitur dapibus, ex massa convallis nibh, et venenatis
+    leo leo sit amet nisl. Lorem ipsum dolor sit amet, consectetur adipiscing
+    elit. Quisque sed mi eu mi rutrum accumsan vel non massa. Nunc condimentum,
+    arcu eget interdum hendrerit, ipsum mi pretium felis, ut mollis erat metus
+    non est. Donec eu sapien id urna lobortis eleifend et eu ipsum. Mauris
+    purus dolor, consequat ac nulla a, vehicula sollicitudin nulla.
+    Phasellus a congue diam. Curabitur sed orci at sem laoreet facilisis eget
+    quis est. Pellentesque habitant morbi tristique senectus et netus et
+    malesuada fames ac turpis egestas. Maecenas justo tellus, efficitur id
+    velit at, mollis pellentesque mi. Vivamus maximus nibh et ipsum porttitor
+    facilisis. Curabitur cursus lobortis erat. Sed vitae eros et dolor feugiat
+    consequat. In ac massa in odio gravida dignissim. Praesent aliquam gravida
+    ullamcorper.
+    Etiam feugiat sit amet odio sed tincidunt. Duis dolor odio, posuere at
+    pretium sed, dignissim eu diam. Aenean eu convallis orci, vitae finibus
+    erat. Aliquam nec mollis tellus. Morbi luctus sed quam et vestibulum.
+    Praesent id diam tempus, consectetur tortor vel, auctor orci. Aliquam
+    congue ex eu sagittis sodales. Suspendisse non convallis nulla. Praesent
+    elementum semper augue, et fringilla risus ullamcorper id. Fusce eu lorem
+    sit amet augue fermentum tincidunt. In aliquam libero sit amet dui rhoncus,
+    ac scelerisque sem porttitor. Cras venenatis, nisi quis ullamcorper
+    dapibus, odio dolor rutrum magna, vel pellentesque sem lectus in tellus.
+    Proin faucibus leo iaculis nulla egestas molestie.
+    Phasellus vitae tortor vitae erat elementum feugiat vel vel enim. Phasellus
+    fringilla lacus sed venenatis dapibus. Phasellus sagittis vel neque ut
+    varius. Proin aliquam, lectus sit amet auctor finibus, lorem libero
+    pellentesque turpis, ac condimentum augue felis sit amet sem. Pellentesque
+    pharetra nisl nec est congue, in posuere felis maximus. In ut nulla
+    sodales, pharetra neque et, venenatis dui. Mauris imperdiet, arcu vel
+    hendrerit vehicula, elit massa consectetur purus, eu blandit nunc orci sit
+    amet turpis. Vestibulum ultricies id lorem id maximus. Pellentesque
+    feugiat, lacus et aliquet consequat, mi leo vehicula justo, dapibus dictum
+    mi quam convallis magna. Quisque id pulvinar dui, consequat gravida nisl.
+    Nam nec justo venenatis, tincidunt enim a, iaculis odio. Maecenas eget
+    lorem posuere, euismod nisl vel, pulvinar ex. Maecenas vitae risus ipsum.
+    Proin congue sem ante, sit amet sagittis odio mattis sit amet. Nullam et
+    nisi nulla.
+    Donec vel hendrerit metus. Praesent quis finibus erat. Aliquam erat
+    volutpat. Fusce sit amet ultricies tellus, vitae dictum dolor. Morbi auctor
+    dolor vel ligula pretium aliquam. Aenean lobortis vel magna vel ultricies.
+    Aenean porta urna vitae ornare porta. Quisque pretium dui diam, quis
+    iaculis odio venenatis non. Maecenas at lacus et ligula tincidunt feugiat
+    eu vel ipsum. Proin fermentum elit et quam tempus, eget pulvinar nisl
+    pharetra.
+    Mauris sodales tempus erat in lobortis. Duis vitae lacinia sapien.
+    Pellentesque vitae massa eget orci sodales aliquet. Orci varius natoque
+    penatibus et magnis dis parturient montes, nascetur ridiculus mus. Fusce
+    nisi arcu, egestas vel consectetur eu, auctor et metus. In ultricies ligula
+    felis, vitae pellentesque dolor tempor ac. Praesent mi magna, ultrices ut
+    ultrices vel, sollicitudin a leo.
+    Nam porta, nisi in scelerisque consequat, leo lacus accumsan massa,
+    venenatis faucibus tellus quam eget tellus. Curabitur pulvinar, tellus ac
+    facilisis consectetur, lacus lacus venenatis est, eu pretium orci augue
+    gravida nunc. Aenean odio tellus, facilisis et finibus id, varius vitae
+    diam. Aenean at suscipit sem. Suspendisse porta neque at nibh semper, sit
+    amet suscipit libero egestas. Donec commodo vitae justo vitae laoreet.
+    Suspendisse dignissim erat id ante maximus porta. Curabitur hendrerit
+    maximus odio, et maximus felis malesuada eu. Integer dapibus finibus diam,
+    quis convallis metus bibendum non.
+    In vel vulputate nisi, non lacinia nunc. Nullam vitae ligula finibus,
+    varius arcu in, pellentesque ipsum. Morbi vel velit tincidunt quam cursus
+    lacinia non in neque. Suspendisse id feugiat nibh. Vestibulum egestas eu
+    leo viverra fringilla. Curabitur ultrices sollicitudin libero, non sagittis
+    felis consectetur id. Aenean non metus eget leo ornare porta sed in metus.
+    Nullam quis fermentum sapien, sit amet sodales mi. Maecenas nec purus urna.
+    Phasellus condimentum enim nec magna convallis, eu lacinia libero
+    scelerisque. Suspendisse justo libero, maximus in auctor id, euismod quis
+    risus. Nam eget augue diam. Ut id risus pulvinar elit consectetur varius.
+    Aliquam tincidunt tortor pretium feugiat tempor. Nunc nec feugiat ex.
+    Ut pulvinar augue eget pharetra vehicula. Phasellus malesuada tempor sem,
+    ut tincidunt velit convallis in. Vivamus luctus libero vitae massa tempus,
+    id elementum urna iaculis. Sed eleifend quis purus quis convallis. In
+    rhoncus interdum mollis. Pellentesque dictum euismod felis, eget lacinia
+    elit blandit vel. Praesent elit velit, pharetra a sodales in, cursus vitae
+    tortor. In vitae scelerisque tellus.
+    """

benchmark/utils/main.swift

@@ -52,10 +52,7 @@ import Chars
 import ClassArrayGetter
 import CodableTest
 import Combos
-import CreateObjects
-import CxxSetToCollection
-import CxxStringConversion
-import CxxVectorSum
+import CountAlgo
 import DataBenchmarks
 import DeadArray
 import DevirtualizeProtocolComposition
@@ -244,6 +241,7 @@ register(CharacterRecognizer.benchmarks)
 register(Chars.benchmarks)
 register(CodableTest.benchmarks)
 register(Combos.benchmarks)
+register(CountAlgo.benchmarks)
 register(ClassArrayGetter.benchmarks)
 register(CreateObjects.benchmarks)
 register(CxxSetToCollection.benchmarks)

stdlib/public/core/SequenceAlgorithms.swift

@@ -572,6 +572,50 @@ extension Sequence where Element: Equatable {
   }
 }
 
+//===----------------------------------------------------------------------===//
+// count(where:)
+//===----------------------------------------------------------------------===//
+
+extension Sequence {
+  /// Returns the number of elements in the sequence that satisfy the given
+  /// predicate.
+  ///
+  /// You can use this method to count the number of elements that pass a test.
+  /// The following example finds the number of names that are fewer than
+  /// five characters long:
+  ///
+  ///     let names = ["Jacqueline", "Ian", "Amy", "Juan", "Soroush", "Tiffany"]
+  ///     let shortNameCount = names.count(where: { $0.count < 5 })
+  ///     // shortNameCount == 3
+  ///
+  /// To find the number of times a specific element appears in the sequence,
+  /// use the equal to operator (`==`) in the closure to test for a match.
+  ///
+  ///     let birds = ["duck", "duck", "duck", "duck", "goose"]
+  ///     let duckCount = birds.count(where: { $0 == "duck" })
+  ///     // duckCount == 4
+  ///
+  /// The sequence must be finite.
+  ///
+  /// - Parameter predicate: A closure that takes each element of the sequence
+  ///   as its argument and returns a Boolean value indicating whether
+  ///   the element should be included in the count.
+  /// - Returns: The number of elements in the sequence that satisfy the given
+  ///   predicate.
+  @inlinable
+  public func count(
+    where predicate: (Element) throws -> Bool
+  ) rethrows -> Int {
+    var count = 0
+    for e in self {
+      if try predicate(e) {
+        count += 1
+      }
+    }
+    return count
+  }
+}
+
 //===----------------------------------------------------------------------===//
 // reduce()
 //===----------------------------------------------------------------------===//

validation-test/stdlib/SequenceType.swift.gyb

@@ -628,6 +628,21 @@ SequenceTypeTests.test("allSatisfy/Predicate") {
   }
 }
 
+//===----------------------------------------------------------------------===//
+// count(where:)
+//===----------------------------------------------------------------------===//
+
+SequenceTypeTests.test("count/Predicate") {
+  for test in predicateCountTests {
+    let s = MinimalSequence<OpaqueValue<Int>>(
+      elements: test.sequence.map { OpaqueValue($0) })
+    expectEqual(
+      test.expected,
+      s.count(where: { test.includeElement($0.value) }),
+      stackTrace: SourceLocStack().with(test.loc))
+  }
+}
+
 //===----------------------------------------------------------------------===//
 // reduce()
 //===----------------------------------------------------------------------===//