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[stdlib] Adopt conditional conformance for Indices, Slice, ReversedCollection (#12913)

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* Refactor Indices and Slice to use conditional conformance

* Replace ReversedRandomAccessCollection with a conditional extension

* Refactor some types into struct+extensions

* Revise Slice documentation

* Fix test cases for adoption of conditional conformances.

* [RangeReplaceableCollection] Eliminate unnecessary slicing subscript operator.

* Add -enable-experimental-conditional-conformances to test.

* Gruesome workaround for crasher in MutableSlice tests
This commit is contained in:
Ben Cohen
2017-11-30 09:10:22 -08:00
committed by GitHub
parent eea5e5db47
commit c4f0b5fe94
25 changed files with 347 additions and 680 deletions
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47
stdlib/public/core/RandomAccessCollection.swift
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@@ -38,7 +38,8 @@ public typealias RandomAccessIndexable = RandomAccessCollection
/// collection, either the index for your custom type must conform to the
/// `Strideable` protocol or you must implement the `index(_:offsetBy:)` and
/// `distance(from:to:)` methods with O(1) efficiency.
public protocol RandomAccessCollection : BidirectionalCollection
public protocol RandomAccessCollection: BidirectionalCollection
where SubSequence: RandomAccessCollection, Indices: RandomAccessCollection
{
// FIXME(ABI): Associated type inference requires this.
associatedtype Element
@@ -46,15 +47,11 @@ public protocol RandomAccessCollection : BidirectionalCollection
// FIXME(ABI): Associated type inference requires this.
associatedtype Index
/// A collection that represents a contiguous subrange of the collection's
/// elements.
associatedtype SubSequence : RandomAccessCollection
= RandomAccessSlice<Self>
// FIXME(ABI): Associated type inference requires this.
associatedtype SubSequence = Slice<Self>
/// A type that represents the indices that are valid for subscripting the
/// collection, in ascending order.
associatedtype Indices : RandomAccessCollection
= DefaultRandomAccessIndices<Self>
// FIXME(ABI): Associated type inference requires this.
associatedtype Indices = DefaultIndices<Self>
/// The indices that are valid for subscripting the collection, in ascending
/// order.
@@ -108,38 +105,6 @@ public protocol RandomAccessCollection : BidirectionalCollection
var endIndex: Index { get }
}
/// Supply the default "slicing" `subscript` for `RandomAccessCollection`
/// models that accept the default associated `SubSequence`,
/// `RandomAccessSlice<Self>`.
extension RandomAccessCollection where SubSequence == RandomAccessSlice<Self> {
/// Accesses a contiguous subrange of the collection's elements.
///
/// The accessed slice uses the same indices for the same elements as the
/// original collection uses. Always use the slice's `startIndex` property
/// instead of assuming that its indices start at a particular value.
///
/// This example demonstrates getting a slice of an array of strings, finding
/// the index of one of the strings in the slice, and then using that index
/// in the original array.
///
/// let streets = ["Adams", "Bryant", "Channing", "Douglas", "Evarts"]
/// let streetsSlice = streets[2 ..< streets.endIndex]
/// print(streetsSlice)
/// // Prints "["Channing", "Douglas", "Evarts"]"
///
/// let index = streetsSlice.index(of: "Evarts") // 4
/// print(streets[index!])
/// // Prints "Evarts"
///
/// - Parameter bounds: A range of the collection's indices. The bounds of
/// the range must be valid indices of the collection.
@_inlineable
public subscript(bounds: Range<Index>) -> RandomAccessSlice<Self> {
_failEarlyRangeCheck(bounds, bounds: startIndex..<endIndex)
return RandomAccessSlice(base: self, bounds: bounds)
}
}
// TODO: swift-3-indexing-model - Make sure RandomAccessCollection has
// documented complexity guarantees, e.g. for index(_:offsetBy:).