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72 lines
2.9 KiB
Swift
72 lines
2.9 KiB
Swift
//===----------------------------------------------------------------------===//
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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) 2016 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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/// A collection that supports efficient random access index traversal.
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///
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/// - Important: In most cases, it's best to ignore this protocol and use
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/// `RandomAccessCollection` instead, as it has a more complete interface.
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public protocol RandomAccessIndexable : BidirectionalIndexable {
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// FIXME(ABI)(compiler limitation): there is no reason for this protocol
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// to exist apart from missing compiler features that we emulate with it.
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//
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// This protocol is almost an implementation detail of the standard
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// library.
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}
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/// A collection that supports efficient random access index traversal.
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///
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/// - Note: the fundamental difference between
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/// `RandomAccessCollection` and `BidirectionalCollection` is that
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/// the following are O(N) in `BidirectionalCollection` but O(1) in
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/// `RandomAccessCollection`:
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///
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/// - `c.count`
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/// - `c.index(i, offsetBy: n)`
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/// - `c.index(i, offsetBy: n, limitedBy: l)`
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/// - `c.distance(from: i, to: j)`
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public protocol RandomAccessCollection :
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RandomAccessIndexable, BidirectionalCollection
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{
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associatedtype SubSequence : RandomAccessIndexable, BidirectionalCollection
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= RandomAccessSlice<Self>
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// FIXME(compiler limitation):
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// associatedtype SubSequence : RandomAccessCollection
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associatedtype Indices : RandomAccessIndexable, BidirectionalCollection
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= DefaultRandomAccessIndices<Self>
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// FIXME(compiler limitation):
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// associatedtype Indices : RandomAccessCollection
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}
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/// Supply the default "slicing" `subscript` for `RandomAccessCollection`
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/// models that accept the default associated `SubSequence`,
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/// `RandomAccessSlice<Self>`.
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extension RandomAccessCollection where SubSequence == RandomAccessSlice<Self> {
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public subscript(bounds: Range<Index>) -> RandomAccessSlice<Self> {
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_failEarlyRangeCheck(bounds, bounds: startIndex..<endIndex)
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return RandomAccessSlice(base: self, bounds: bounds)
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}
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}
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/// Default implementation for random access collections.
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extension RandomAccessCollection {
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// TODO: swift-3-indexing-model - implement optimized version of the following
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// (also un-xfail corresponding test in validation-test/stdlib/Index.swift.gyb)
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//func index(i: Index, offsetBy n: IndexDistance) -> Index
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//@warn_unused_result
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//func index(
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// i: Index, offsetBy n: IndexDistance, limitedBy limit: Index
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//) -> Index?
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//distance(from start: Index, to end: Index) -> IndexDistance
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}
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