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Refactor Mirror to reduce metadata allocation #32041
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airspeedswift
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airspeedswift:such-lazy-children
May 28, 2020
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,197 @@ | ||
| ////===--- _EitherSequence.swift - A sequence type-erasing two sequences -----===// | ||
| //// | ||
| //// This source file is part of the Swift.org open source project | ||
| //// | ||
| //// Copyright (c) 2014 - 2017 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 | ||
| //// | ||
| ////===----------------------------------------------------------------------===// | ||
|
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| // Not public stdlib API, currently used in Mirror.children implementation. | ||
|
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| internal enum _Either<Left, Right> { | ||
| case left(Left), right(Right) | ||
| } | ||
|
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| extension _Either { | ||
| internal init(_ left: Left, or other: Right.Type) { self = .left(left) } | ||
| internal init(_ left: Left) { self = .left(left) } | ||
| internal init(_ right: Right) { self = .right(right) } | ||
| } | ||
|
|
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| extension _Either: Equatable where Left: Equatable, Right: Equatable { | ||
| internal static func == (lhs: Self, rhs: Self) -> Bool { | ||
| switch (lhs, rhs) { | ||
| case let (.left(l), .left(r)): return l == r | ||
| case let (.right(l), .right(r)): return l == r | ||
| case (.left, .right), (.right, .left): return false | ||
| } | ||
| } | ||
| } | ||
|
|
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| extension _Either: Comparable where Left: Comparable, Right: Comparable { | ||
| internal static func < (lhs: Self, rhs: Self) -> Bool { | ||
| switch (lhs, rhs) { | ||
| case let (.left(l), .left(r)): return l < r | ||
| case let (.right(l), .right(r)): return l < r | ||
| case (.left, .right): return true | ||
| case (.right, .left): return false | ||
| } | ||
| } | ||
| } | ||
|
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| /// A sequence that type erases two sequences. A lighter-weight alternative to | ||
| /// AnySequence when more can be statically known, and which is more easily | ||
| /// specialized. | ||
| /// | ||
| /// If you only know about one of the types, the second one can be | ||
| /// AnySequence, giving you a fast path for the known one. | ||
| /// | ||
| /// If you have 3+ types to erase, you can nest them. | ||
| typealias _EitherSequence<L: Sequence, R: Sequence> = | ||
| _Either<L,R> where L.Element == R.Element | ||
|
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| extension _EitherSequence { | ||
| internal struct Iterator { | ||
| var left: Left.Iterator? | ||
| var right: Right.Iterator? | ||
| } | ||
| } | ||
|
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| extension _Either.Iterator: IteratorProtocol { | ||
| internal typealias Element = Left.Element | ||
|
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| internal mutating func next() -> Element? { | ||
| left?.next() ?? right?.next() | ||
| } | ||
| } | ||
|
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| extension _EitherSequence: Sequence { | ||
| internal typealias Element = Left.Element | ||
|
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| internal func makeIterator() -> Iterator { | ||
| switch self { | ||
| case let .left(l): | ||
| return Iterator(left: l.makeIterator(), right: nil) | ||
| case let .right(r): | ||
| return Iterator(left: nil, right: r.makeIterator()) | ||
| } | ||
| } | ||
| } | ||
|
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| internal typealias _EitherCollection< | ||
| T: Collection, U: Collection | ||
| > = _EitherSequence<T,U> where T.Element == U.Element | ||
|
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| extension _EitherCollection: Collection { | ||
| internal typealias Index = _Either<Left.Index, Right.Index> | ||
|
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| internal var startIndex: Index { | ||
| switch self { | ||
| case let .left(s): return .left(s.startIndex) | ||
| case let .right(s): return .right(s.startIndex) | ||
| } | ||
| } | ||
|
|
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| internal var endIndex: Index { | ||
| switch self { | ||
| case let .left(s): return .left(s.endIndex) | ||
| case let .right(s): return .right(s.endIndex) | ||
| } | ||
| } | ||
|
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| internal subscript(position: Index) -> Element { | ||
| switch (self,position) { | ||
| case let (.left(s),.left(i)): return s[i] | ||
| case let (.right(s),.right(i)): return s[i] | ||
| default: fatalError("_EitherCollecton: Sequence used with other index type") | ||
| } | ||
| } | ||
|
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| internal func index(after i: Index) -> Index { | ||
| switch (self,i) { | ||
| case let (.left(s),.left(i)): return .left(s.index(after: i)) | ||
| case let (.right(s),.right(i)): return .right(s.index(after: i)) | ||
| default: fatalError("_EitherCollecton: wrong type of index used") | ||
| } | ||
| } | ||
|
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| internal func index( | ||
| _ i: Index, | ||
| offsetBy distance: Int, | ||
| limitedBy limit: Index | ||
| ) -> Index? { | ||
| switch (self,i,limit) { | ||
| case let (.left(s),.left(i),.left(limit)): | ||
| return s.index(i, offsetBy: distance, limitedBy: limit).map { .left($0) } | ||
| case let (.right(s),.right(i),.right(limit)): | ||
| return s.index(i, offsetBy: distance, limitedBy: limit).map { .right($0) } | ||
| default: fatalError("_EitherCollecton: wrong type of index used") | ||
| } | ||
| } | ||
|
|
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| internal func index(_ i: Index, offsetBy distance: Int) -> Index { | ||
| switch (self,i) { | ||
| case let (.left(s),.left(i)): return .left(s.index(i, offsetBy: distance)) | ||
| case let (.right(s),.right(i)): return .right(s.index(i, offsetBy: distance)) | ||
| default: fatalError("_EitherCollecton: wrong type of index used") | ||
| } | ||
| } | ||
|
|
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| internal func distance(from start: Index, to end: Index) -> Int { | ||
| switch (self,start,end) { | ||
| case let (.left(s),.left(i),.left(j)): | ||
| return s.distance(from: i, to: j) | ||
| case let (.right(s),.right(i),.right(j)): | ||
| return s.distance(from: i, to: j) | ||
| default: fatalError("_EitherCollecton: wrong type of index used") | ||
| } | ||
| } | ||
| } | ||
|
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| internal typealias _EitherBidirectionalCollection< | ||
| L: BidirectionalCollection, R: BidirectionalCollection | ||
| > = _Either<L,R> where L.Element == R.Element | ||
|
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| extension _EitherBidirectionalCollection: BidirectionalCollection { | ||
| internal func index(before i: Index) -> Index { | ||
| switch (self,i) { | ||
| case let (.left(s),.left(i)): return .left(s.index(before: i)) | ||
| case let (.right(s),.right(i)): return .right(s.index(before: i)) | ||
| default: fatalError("_EitherCollecton: wrong type of index used") | ||
| } | ||
| } | ||
| } | ||
|
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| internal typealias _EitherRandomAccessCollection< | ||
| L: RandomAccessCollection, R: RandomAccessCollection | ||
| > = _Either<L,R> where L.Element == R.Element | ||
|
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| extension _EitherRandomAccessCollection: RandomAccessCollection { } | ||
|
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| extension _Either { | ||
| init<T, C: Collection>( | ||
| _ collection: C | ||
| ) where Right == AnyCollection<T>, C.Element == T { | ||
| self = .right(AnyCollection(collection)) | ||
| } | ||
| } | ||
|
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| extension AnyCollection { | ||
| init<L: Collection,R: Collection>( | ||
| _ other: _Either<L,R> | ||
| ) where L.Element == Element, R.Element == Element { | ||
| // Strip away the Either and put the actual collection into the existential, | ||
| // trying to use the custom initializer from another AnyCollection. | ||
| switch other { | ||
| case let .left(l as Self): self = .init(l) | ||
| case let .right(r as Self): self = .init(r) | ||
| case let .left(l): self = .init(l) | ||
| case let .right(r): self = .init(r) | ||
| } | ||
| } | ||
| } | ||
|
|
||
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I think we can drop
Tby expressing this asRight == AnyCollection<C.Element>