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[stdlib] Adding RangeReplaceable.filter returning Self #9741

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Merged
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May 18, 2017
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[stdlib] Adding RangeReplaceable.filter returning Self #9741

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10 changes: 10 additions & 0 deletions stdlib/public/core/Arrays.swift.gyb
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Expand Up @@ -1574,6 +1574,16 @@ extension ${Self} : RangeReplaceableCollection, _ArrayProtocol {
}
}

// Since RangeReplaceableCollection now has a version of filter that is less
// efficient, we should make the default implementation coming from Sequence
// preferred.
@_inlineable
public func filter(
_ isIncluded: (Element) throws -> Bool
) rethrows -> [Element] {
return try _filter(isIncluded)
}

//===--- algorithms -----------------------------------------------------===//

@_inlineable
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25 changes: 25 additions & 0 deletions stdlib/public/core/RangeReplaceableCollection.swift.gyb
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Expand Up @@ -1212,6 +1212,31 @@ public func += <
lhs.append(contentsOf: rhs)
}

extension RangeReplaceableCollection {
/// Returns a new collection of the same type containing, in order, the
/// elements of the original collection that satisfy the given predicate.
///
/// In this example, `filter(_:)` is used to include only names shorter than
/// five characters.
///
/// let cast = ["Vivien", "Marlon", "Kim", "Karl"]
/// let shortNames = cast.filter { $0.count < 5 }
/// print(shortNames)
/// // Prints "["Kim", "Karl"]"
///
/// - Parameter isIncluded: A closure that takes an element of the
/// sequence as its argument and returns a Boolean value indicating
/// whether the element should be included in the returned array.
/// - Returns: An array of the elements that `isIncluded` allowed.
@_inlineable
@available(swift, introduced: 4.0)
public func filter(
_ isIncluded: (Element) throws -> Bool
) rethrows -> Self {
return try Self(self.lazy.filter(isIncluded))
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Probably worth checking that this is just as fast as a hand-rolled loop with append. It ought to be, and this is definitely the right way to code it, but worth checking. I'll add a benchmark – doesn't need to hold this up though.

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One cannot regress something that does not exist. 🤷‍♂️

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Here is the snippet I played with:

@inline(never)
public func iteration<
  C : RangeReplaceableCollection
>(_ xs: C, _ f: (C.Element) -> Bool) -> C {
    var result = C()
    var iterator = xs.makeIterator()
    while let element = iterator.next() {
      if f(element) {
        result.append(element)
      }
    }
    return result
}

@inline(never)
public func lazyFilter<
  C : RangeReplaceableCollection
>(_ xs: C, _ f: (C.Element) -> Bool) -> C {
  return C(xs.lazy.filter(f))
}


for _ in 0..<1_000 {
  /*_ = iteration(Array(0..<10000)) { $0 % 2 == 0 }*/
  _ = lazyFilter(Array(0..<10000)) { $0 % 2 == 0 }
}

Commenting one and uncommenting the other gives these results on my machine:

# lazyFilter                                                                                                                        
swiftc -swift-version 3 -O ../filter.swift -o ../filter && time ../filter
../filter  0.59s user 0.00s system 99% cpu 0.604 total

# iteration
swiftc -swift-version 3 -O ../filter.swift -o ../filter && time ../filter
../filter  1.45s user 0.00s system 99% cpu 1.462 total

#lazyFilter                                                                                                    
swiftc -swift-version 4 -O ../filter.swift -o ../filter && time ../filter
../filter  0.60s user 0.00s system 99% cpu 0.604 total

# iteration                                                                                                                        
swiftc -swift-version 4 -O ../filter.swift -o ../filter && time ../filter
../filter  1.46s user 0.00s system 99% cpu 1.469 total

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Also both IR and SIL look better in case of lazyFilter.

}
}

@available(*, unavailable, renamed: "RangeReplaceableCollection")
public typealias RangeReplaceableCollectionType = RangeReplaceableCollection

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7 changes: 7 additions & 0 deletions stdlib/public/core/Sequence.swift
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Expand Up @@ -877,6 +877,13 @@ extension Sequence {
public func filter(
_ isIncluded: (Element) throws -> Bool
) rethrows -> [Element] {
return try _filter(isIncluded)
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This will mean ContiguousArray and ArraySlice will also return an Array from filter, not Self? Which is... probably the right thing? Worth checking my thinking though.

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That's what they have been doing all along. filter is not redefined anywhere near array types. They all inherit the default Sequence implementation.

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Oh, I see what you mean here... The line you commented on is misleading, but yeah, even with the addition of a new overload, they will still return [T].

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Right. I was just questioning whether this is the right thing. I think it is for those two types specifically.

}

@_transparent
public func _filter(
_ isIncluded: (Element) throws -> Bool
) rethrows -> [Element] {

var result = ContiguousArray<Element>()

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29 changes: 29 additions & 0 deletions test/stdlib/RangeReplaceableFilterCompatibility.swift
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@@ -0,0 +1,29 @@
// RUN: rm -rf %t ; mkdir -p %t
// RUN: %target-build-swift %s -o %t/a.out3 -swift-version 3 && %target-run %t/a.out3
// RUN: %target-build-swift %s -o %t/a.out4 -swift-version 4 && %target-run %t/a.out4

import StdlibUnittest

var tests = TestSuite("RangeReplaceableFilterCompatibility")

tests.test("String.filter return type") {
var filtered = "Hello, World".filter { $0 < "A" }
#if swift(>=4)
expectType(String.self, &filtered)
#else
expectType([Character].self, &filtered)
#endif
}

tests.test("Array.filter return type") {
var filtered = Array(0..<10).filter { $0 % 2 == 0 }
expectType([Int].self, &filtered)
}

tests.test("String.filter can return [Character]") {
let filtered = "Hello, World".filter { "A" <= $0 && $0 <= "Z"} as [Character]
expectEqualSequence("HW", filtered)
}


runAllTests()