-
Notifications
You must be signed in to change notification settings - Fork 10.3k
/
Filter.swift
345 lines (309 loc) · 11 KB
/
Filter.swift
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
//===--- Filter.swift -----------------------------------------*- swift -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
/// A sequence whose elements consist of the elements of some base
/// sequence that also satisfy a given predicate.
///
/// - Note: `s.lazy.filter { ... }`, for an arbitrary sequence `s`,
/// is a `LazyFilterSequence`.
@_fixed_layout // lazy-performance
public struct LazyFilterSequence<Base: Sequence> {
@usableFromInline // lazy-performance
internal var _base: Base
/// The predicate used to determine which elements produced by
/// `base` are also produced by `self`.
@usableFromInline // lazy-performance
internal let _predicate: (Base.Element) -> Bool
/// Creates an instance consisting of the elements `x` of `base` for
/// which `isIncluded(x) == true`.
@inlinable // lazy-performance
public // @testable
init(_base base: Base, _ isIncluded: @escaping (Base.Element) -> Bool) {
self._base = base
self._predicate = isIncluded
}
}
extension LazyFilterSequence {
/// An iterator over the elements traversed by some base iterator that also
/// satisfy a given predicate.
///
/// - Note: This is the associated `Iterator` of `LazyFilterSequence`
/// and `LazyFilterCollection`.
@_fixed_layout // lazy-performance
public struct Iterator {
/// The underlying iterator whose elements are being filtered.
public var base: Base.Iterator { return _base }
@usableFromInline // lazy-performance
internal var _base: Base.Iterator
@usableFromInline // lazy-performance
internal let _predicate: (Base.Element) -> Bool
/// Creates an instance that produces the elements `x` of `base`
/// for which `isIncluded(x) == true`.
@inlinable // lazy-performance
internal init(_base: Base.Iterator, _ isIncluded: @escaping (Base.Element) -> Bool) {
self._base = _base
self._predicate = isIncluded
}
}
}
extension LazyFilterSequence.Iterator: IteratorProtocol, Sequence {
public typealias Element = Base.Element
/// Advances to the next element and returns it, or `nil` if no next element
/// exists.
///
/// Once `nil` has been returned, all subsequent calls return `nil`.
///
/// - Precondition: `next()` has not been applied to a copy of `self`
/// since the copy was made.
@inlinable // lazy-performance
public mutating func next() -> Element? {
while let n = _base.next() {
if _predicate(n) {
return n
}
}
return nil
}
}
extension LazyFilterSequence: Sequence {
public typealias Element = Base.Element
/// Returns an iterator over the elements of this sequence.
///
/// - Complexity: O(1).
@inlinable // lazy-performance
public __consuming func makeIterator() -> Iterator {
return Iterator(_base: _base.makeIterator(), _predicate)
}
@inlinable
public func _customContainsEquatableElement(_ element: Element) -> Bool? {
// optimization to check the element first matches the predicate
guard _predicate(element) else { return false }
return _base._customContainsEquatableElement(element)
}
}
extension LazyFilterSequence: LazySequenceProtocol { }
/// A lazy `Collection` wrapper that includes the elements of an
/// underlying collection that satisfy a predicate.
///
/// - Note: The performance of accessing `startIndex`, `first`, any methods
/// that depend on `startIndex`, or of advancing an index depends
/// on how sparsely the filtering predicate is satisfied, and may not offer
/// the usual performance given by `Collection`. Be aware, therefore, that
/// general operations on `LazyFilterCollection` instances may not have the
/// documented complexity.
public typealias LazyFilterCollection<T: Collection> = LazyFilterSequence<T>
extension LazyFilterCollection: Collection {
public typealias SubSequence = LazyFilterCollection<Base.SubSequence>
// Any estimate of the number of elements that pass `_predicate` requires
// iterating the collection and evaluating each element, which can be costly,
// is unexpected, and usually doesn't pay for itself in saving time through
// preventing intermediate reallocations. (SR-4164)
@inlinable // lazy-performance
public var underestimatedCount: Int { return 0 }
/// A type that represents a valid position in the collection.
///
/// Valid indices consist of the position of every element and a
/// "past the end" position that's not valid for use as a subscript.
public typealias Index = Base.Index
/// The position of the first element in a non-empty collection.
///
/// In an empty collection, `startIndex == endIndex`.
///
/// - Complexity: O(*n*), where *n* is the ratio between unfiltered and
/// filtered collection counts.
@inlinable // lazy-performance
public var startIndex: Index {
var index = _base.startIndex
while index != _base.endIndex && !_predicate(_base[index]) {
_base.formIndex(after: &index)
}
return index
}
/// The collection's "past the end" position---that is, the position one
/// greater than the last valid subscript argument.
///
/// `endIndex` is always reachable from `startIndex` by zero or more
/// applications of `index(after:)`.
@inlinable // lazy-performance
public var endIndex: Index {
return _base.endIndex
}
// TODO: swift-3-indexing-model - add docs
@inlinable // lazy-performance
public func index(after i: Index) -> Index {
var i = i
formIndex(after: &i)
return i
}
@inlinable // lazy-performance
public func formIndex(after i: inout Index) {
// TODO: swift-3-indexing-model: _failEarlyRangeCheck i?
var index = i
_precondition(index != _base.endIndex, "Can't advance past endIndex")
repeat {
_base.formIndex(after: &index)
} while index != _base.endIndex && !_predicate(_base[index])
i = index
}
@inline(__always)
@inlinable // lazy-performance
internal func _advanceIndex(_ i: inout Index, step: Int) {
repeat {
_base.formIndex(&i, offsetBy: step)
} while i != _base.endIndex && !_predicate(_base[i])
}
@inline(__always)
@inlinable // lazy-performance
internal func _ensureBidirectional(step: Int) {
// FIXME: This seems to be the best way of checking whether _base is
// forward only without adding an extra protocol requirement.
// index(_:offsetBy:limitedBy:) is chosen becuase it is supposed to return
// nil when the resulting index lands outside the collection boundaries,
// and therefore likely does not trap in these cases.
if step < 0 {
_ = _base.index(
_base.endIndex, offsetBy: step, limitedBy: _base.startIndex)
}
}
@inlinable // lazy-performance
public func distance(from start: Index, to end: Index) -> Int {
// The following line makes sure that distance(from:to:) is invoked on the
// _base at least once, to trigger a _precondition in forward only
// collections.
_ = _base.distance(from: start, to: end)
var _start: Index
let _end: Index
let step: Int
if start > end {
_start = end
_end = start
step = -1
}
else {
_start = start
_end = end
step = 1
}
var count = 0
while _start != _end {
count += step
formIndex(after: &_start)
}
return count
}
@inlinable // lazy-performance
public func index(_ i: Index, offsetBy n: Int) -> Index {
var i = i
let step = n.signum()
// The following line makes sure that index(_:offsetBy:) is invoked on the
// _base at least once, to trigger a _precondition in forward only
// collections.
_ensureBidirectional(step: step)
for _ in 0 ..< abs(numericCast(n)) {
_advanceIndex(&i, step: step)
}
return i
}
@inlinable // lazy-performance
public func formIndex(_ i: inout Index, offsetBy n: Int) {
i = index(i, offsetBy: n)
}
@inlinable // lazy-performance
public func index(
_ i: Index, offsetBy n: Int, limitedBy limit: Index
) -> Index? {
var i = i
let step = n.signum()
// The following line makes sure that index(_:offsetBy:limitedBy:) is
// invoked on the _base at least once, to trigger a _precondition in
// forward only collections.
_ensureBidirectional(step: step)
for _ in 0 ..< abs(numericCast(n)) {
if i == limit {
return nil
}
_advanceIndex(&i, step: step)
}
return i
}
@inlinable // lazy-performance
public func formIndex(
_ i: inout Index, offsetBy n: Int, limitedBy limit: Index
) -> Bool {
if let advancedIndex = index(i, offsetBy: n, limitedBy: limit) {
i = advancedIndex
return true
}
i = limit
return false
}
/// Accesses the element at `position`.
///
/// - Precondition: `position` is a valid position in `self` and
/// `position != endIndex`.
@inlinable // lazy-performance
public subscript(position: Index) -> Element {
return _base[position]
}
@inlinable // lazy-performance
public subscript(bounds: Range<Index>) -> SubSequence {
return SubSequence(_base: _base[bounds], _predicate)
}
@inlinable
public func _customLastIndexOfEquatableElement(_ element: Element) -> Index?? {
guard _predicate(element) else { return .some(nil) }
return _base._customLastIndexOfEquatableElement(element)
}
}
extension LazyFilterCollection: LazyCollectionProtocol { }
extension LazyFilterCollection : BidirectionalCollection
where Base : BidirectionalCollection {
@inlinable // lazy-performance
public func index(before i: Index) -> Index {
var i = i
formIndex(before: &i)
return i
}
@inlinable // lazy-performance
public func formIndex(before i: inout Index) {
// TODO: swift-3-indexing-model: _failEarlyRangeCheck i?
var index = i
_precondition(index != _base.startIndex, "Can't retreat before startIndex")
repeat {
_base.formIndex(before: &index)
} while !_predicate(_base[index])
i = index
}
}
extension LazySequenceProtocol {
/// Returns the elements of `self` that satisfy `isIncluded`.
///
/// - Note: The elements of the result are computed on-demand, as
/// the result is used. No buffering storage is allocated and each
/// traversal step invokes `predicate` on one or more underlying
/// elements.
@inlinable // lazy-performance
public __consuming func filter(
_ isIncluded: @escaping (Elements.Element) -> Bool
) -> LazyFilterSequence<Self.Elements> {
return LazyFilterSequence(_base: self.elements, isIncluded)
}
}
extension LazyFilterSequence {
@available(swift, introduced: 5)
public __consuming func filter(
_ isIncluded: @escaping (Element) -> Bool
) -> LazyFilterSequence<Base> {
return LazyFilterSequence(_base: _base) {
isIncluded($0) && self._predicate($0)
}
}
}