[stdlib] Adding RangeReplaceable.filter returning Self #9741
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This overload allows `String.filter` to return a `String`, and not `[Character]`. In the other hand, introduction of this overload makes `[123].filter` somewhat ambiguous in a sence, that the compiler will now prefer an implementatin from a more concrete protocol, which is less efficient for arrays, therefore extra work is needed to make sure Array types fallback to the `Sequence.filter`. Implements: <rdar://problem/32209927>
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airspeedswift
approved these changes
May 18, 2017
| 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.
| @@ -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.
Build comment file:Optimized (O) Regression (1)
Improvement (1)
No Changes (270)
Regression (1)
Improvement (2)
No Changes (269)
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This was referenced May 18, 2017
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This overload allows
String.filterto return aString, and not[Character].In the other hand, introduction of this overload makes
[123].filtersomewhat ambiguous in a sence, that the compiler will now prefer an
implementatin from a more concrete protocol, which is less efficient for
arrays, therefore extra work is needed to make sure Array types fallback
to the
Sequence.filter.Implements: rdar://problem/32209927