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Dave Abrahams
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[stdlib] Add lazy and Array filter algorithm
This came up during API review Swift SVN r18364
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‎stdlib/core/Arrays.swift.gyb

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@@ -232,6 +232,12 @@ extension ${Self} : ArrayType {
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return result
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}
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/// Return a ${Self} containg the elements `x` of `self` for which
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/// `includeElement(x)` is `true`
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func filter(includeElement: (T)->Bool) -> ${Self} {
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return ${Self}(Swift.filter(self, includeElement))
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}
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}
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extension ${Self} : Reflectable {

‎stdlib/core/CMakeLists.txt

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@@ -38,6 +38,7 @@ set(SWIFTLIB_ESSENTIAL
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Dictionary.swift
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EmptyCollection.swift
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Existential.swift
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Filter.swift
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FixedPoint.swift.gyb
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FloatingPoint.swift.gyb
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FloatingPointOperations.swift

‎stdlib/core/Filter.swift

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//===--- Filter.swift - Lazily filter the elements of a Sequence ----------===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See http://swift.org/LICENSE.txt for license information
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// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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/// The `Generator` used by `FilterSequenceView` and
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/// `FilterCollectionView`
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struct FilterGenerator<Base: Generator> : Generator, Sequence {
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mutating func next() -> Base.Element? {
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var n: Base.Element?
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for/*ever*/;; {
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n = _base.next()
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if n ? _include(n!) : true {
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return n
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}
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}
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}
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func generate() -> FilterGenerator {
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return self
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}
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var _base: Base
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var _include: (Base.Element)->Bool
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}
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/// The lazy `Sequence` returned by `filter(c)` where `c` is a
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/// `Sequence`
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struct FilterSequenceView<Base: Sequence> : Sequence {
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func generate() -> FilterGenerator<Base.GeneratorType> {
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return FilterGenerator(_base: _base.generate(), _include: _include)
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}
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var _base: Base
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var _include: (Base.GeneratorType.Element)->Bool
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}
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/// The `IndexType` used for subscripting a `FilterCollectionView`
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struct FilterCollectionViewIndex<Base: Collection> : ForwardIndex {
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func succ() -> FilterCollectionViewIndex {
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for nextPos in _pos.succ().._end {
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if _include(_base[nextPos]) {
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return FilterCollectionViewIndex(
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_pos: nextPos, _end: _end,
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_base: _base, _include: _include)
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}
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}
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return FilterCollectionViewIndex(
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_pos: _end, _end: _end, _base: _base, _include: _include)
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}
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var _pos: Base.IndexType
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var _end: Base.IndexType
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var _base: Base
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var _include: (Base.GeneratorType.Element)->Bool
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}
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func == <Base: Collection>(
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lhs: FilterCollectionViewIndex<Base>,
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rhs: FilterCollectionViewIndex<Base>
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) -> Bool {
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return lhs._pos == rhs._pos
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}
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/// The lazy `Collection` returned by `filter(c)` where `c` is a
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/// `Collection`
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struct FilterCollectionView<Base: Collection> : Collection {
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typealias IndexType = FilterCollectionViewIndex<Base>
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var startIndex: IndexType {
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var first = _base.startIndex
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while first != _base.endIndex {
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if _include(_base[first]) {
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break
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}
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++first
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}
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return FilterCollectionViewIndex(
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_pos: first, _end: _base.endIndex, _base: _base, _include: _include)
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}
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var endIndex: IndexType {
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return FilterCollectionViewIndex(
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_pos: _base.endIndex, _end: _base.endIndex,
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_base: _base, _include: _include)
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}
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subscript(index: IndexType) -> Base.GeneratorType.Element {
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return _base[index._pos]
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}
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func generate() -> FilterGenerator<Base.GeneratorType> {
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return FilterGenerator(_base: _base.generate(), _include: _include)
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}
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var _base: Base
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var _include: (Base.GeneratorType.Element)->Bool
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}
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/// Return a lazy Sequence containing the elements `x` of `source` for
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/// which `includeElement(x)` is `true`
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func filter<S:Sequence>(
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source: S, includeElement: (S.GeneratorType.Element)->Bool
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) -> FilterSequenceView<S> {
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return FilterSequenceView(_base: source, _include: includeElement)
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}
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/// Return a lazy Collection containing the elements `x` of `source` for
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/// which `includeElement(x)` is `true`
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func filter<C:Collection>(
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source: C, includeElement: (C.GeneratorType.Element)->Bool
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) -> FilterCollectionView<C> {
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return FilterCollectionView(_base: source, _include: includeElement)
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}

‎test/stdlib/Array.swift

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@@ -79,5 +79,12 @@ func testCopy() {
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}
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testCopy()
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func testFilter() {
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let a = Array(3..16)
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println(a.filter { $0 % 4 == 0 })
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// CHECK-NEXT: [4, 8, 12]
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}
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testFilter()
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println("done!") // CHECK-NEXT: {{^done!$}}
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‎test/stdlib/Filter.swift

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//===--- Filter.swift - tests for lazy filtering --------------------------===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See http://swift.org/LICENSE.txt for license information
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// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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// RUN: %target-run-simple-swift | FileCheck %s
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// CHECK: testing...
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println("testing...")
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func printlnByGenerating<S: Sequence>(s: S) {
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print("<")
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var prefix = ""
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for x in s {
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print("\(prefix)\(x)")
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prefix = ", "
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}
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println(">")
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}
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func printlnByIndexing<C: Collection>(c: C) {
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printlnByGenerating(
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PermutationGenerator(elements: c, indices: indices(c))
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)
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}
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// Test filtering Collections
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if true {
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let f0 = filter(0..30) { $0 % 7 == 0 }
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// CHECK-NEXT: <0, 7, 14, 21, 28>
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printlnByGenerating(f0)
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// CHECK-NEXT: <0, 7, 14, 21, 28>
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printlnByIndexing(f0)
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// Also try when the first element of the underlying sequence
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// doesn't pass the filter
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let f1 = filter(1..30) { $0 % 7 == 0 }
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// CHECK-NEXT: <7, 14, 21, 28>
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printlnByGenerating(f1)
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// CHECK-NEXT: <7, 14, 21, 28>
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printlnByIndexing(f1)
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}
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// Test filtering Sequences
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if true {
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let f0 = filter((0..30).generate()) { $0 % 7 == 0 }
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// CHECK-NEXT: <0, 7, 14, 21, 28>
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printlnByGenerating(f0)
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// Also try when the first element of the underlying sequence
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// doesn't pass the filter
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let f1 = filter((1..30).generate()) { $0 % 7 == 0 }
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// CHECK-NEXT: <7, 14, 21, 28>
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printlnByGenerating(f1)
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}
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// CHECK-NEXT: all done.
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println("all done.")

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