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Filter.swift
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Filter.swift
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//===--- Filter.swift -----------------------------------------*- swift -*-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
/// A generator that produces the elements produced by some base
/// generator that also satisfy a given predicate.
///
/// - Note: This is the associated `Generator` of `LazyFilterSequence`
/// and `LazyFilterCollection`.
@swift3_migration(renamed="LazyFilterIterator")
public struct LazyFilterGenerator<
Base : GeneratorType
> : GeneratorType, SequenceType {
/// Advances to the next element and returns it, or `nil` if no next
/// element exists.
///
/// - Requires: `next()` has not been applied to a copy of `self`
/// since the copy was made, and no preceding call to `self.next()`
/// has returned `nil`.
public mutating func next() -> Base.Element? {
while let n = _base.next() {
if _predicate(n) {
return n
}
}
return nil
}
/// Creates an instance that produces the elements `x` of `base`
/// for which `predicate(x) == true`.
@swift3_migration(message="use '.lazy.filter' on the sequence")
@available(*, deprecated, message="it will be removed in Swift 3, use '.lazy.filter' on the sequence")
public init(
_ base: Base,
whereElementsSatisfy predicate: (Base.Element) -> Bool
) {
self._base = base
self._predicate = predicate
}
/// The underlying generator whose elements are being filtered
public var base: Base { return _base }
internal var _base: Base
/// The predicate used to determine which elements produced by
/// `base` are also produced by `self`.
internal var _predicate: (Base.Element) -> Bool
}
/// 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`.
public struct LazyFilterSequence<Base : SequenceType>
: LazySequenceType {
/// Returns a generator over the elements of this sequence.
///
/// - Complexity: O(1).
@swift3_migration(renamed="makeIterator()")
public func generate() -> LazyFilterGenerator<Base.Generator> {
return LazyFilterGenerator(
base.generate(), whereElementsSatisfy: _include)
}
/// Creates an instance consisting of the elements `x` of `base` for
/// which `predicate(x) == true`.
public init(
_ base: Base,
whereElementsSatisfy predicate: (Base.Generator.Element) -> Bool
) {
self.base = base
self._include = predicate
}
/// The underlying sequence whose elements are being filtered
public let base: Base
/// The predicate used to determine which elements of `base` are
/// also elements of `self`.
internal let _include: (Base.Generator.Element) -> Bool
}
/// The `Index` used for subscripting a `LazyFilterCollection`.
///
/// The positions of a `LazyFilterIndex` correspond to those positions
/// `p` in its underlying collection `c` such that `c[p]`
/// satisfies the predicate with which the `LazyFilterIndex` was
/// initialized.
///
/// - Note: The performance of advancing a `LazyFilterIndex`
/// depends on how sparsely the filtering predicate is satisfied,
/// and may not offer the usual performance given by models of
/// `ForwardIndexType`.
public struct LazyFilterIndex<
BaseElements: CollectionType
> : ForwardIndexType {
/// Returns the next consecutive value after `self`.
///
/// - Requires: The next value is representable.
///
/// - Complexity: Amortized O(M), where M is the average distance in
/// the base collection between elements that satisfy the
/// predicate.
///
/// - Note: This operation may not satisfy the expected complexity
/// for models of `ForwardIndexType`.
public func successor() -> LazyFilterIndex {
for p in base.successor()..<_baseElements.endIndex {
if _include(_baseElements[p]) {
return LazyFilterIndex(
_baseElements: _baseElements, base: p, _include: _include)
}
}
return LazyFilterIndex(
_baseElements: _baseElements, base: _baseElements.endIndex,
_include: _include)
}
internal let _baseElements: BaseElements
/// The position corresponding to `self` in the underlying collection.
public let base: BaseElements.Index
/// The predicate used to determine which elements of `base` are
/// also elements of `self`.
internal let _include: (BaseElements.Generator.Element) -> Bool
@available(*, unavailable, renamed="BaseElements")
public typealias Base = BaseElements
}
/// Returns `true` iff `lhs` is identical to `rhs`.
@warn_unused_result
public func == <Base : CollectionType>(
lhs: LazyFilterIndex<Base>,
rhs: LazyFilterIndex<Base>
) -> Bool {
return lhs.base == rhs.base
}
/// A lazy `CollectionType` 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 a `LazyFilterIndex` depends
/// on how sparsely the filtering predicate is satisfied, and may not offer
/// the usual performance given by `CollectionType` or `ForwardIndexType`. Be
/// aware, therefore, that general operations on `LazyFilterCollection`
/// instances may not have the documented complexity.
public struct LazyFilterCollection<
Base : CollectionType
> : LazyCollectionType {
/// 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 = LazyFilterIndex<Base>
/// Construct an instance containing the elements of `base` that
/// satisfy `predicate`.
@swift3_migration(message="use '.lazy.filter' on the collection")
@available(*, deprecated, message="it will be removed in Swift 3, use '.lazy.filter' on the collection")
public init(
_ base: Base,
whereElementsSatisfy predicate: (Base.Generator.Element) -> Bool
) {
self._base = base
self._predicate = predicate
}
/// 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.
public var startIndex: Index {
var first = _base.startIndex
while first != _base.endIndex {
if _predicate(_base[first]) {
break
}
first._successorInPlace()
}
return LazyFilterIndex(
_baseElements: _base, base: first, _include: _predicate)
}
/// The collection's "past the end" position.
///
/// `endIndex` is not a valid argument to `subscript`, and is always
/// reachable from `startIndex` by zero or more applications of
/// `successor()`.
///
/// - Complexity: O(1).
public var endIndex: Index {
return LazyFilterIndex(
_baseElements: _base, base: _base.endIndex, _include: _predicate)
}
/// Access the element at `position`.
///
/// - Requires: `position` is a valid position in `self` and
/// `position != endIndex`.
public subscript(position: Index) -> Base.Generator.Element {
return _base[position.base]
}
/// Returns a generator over the elements of this sequence.
///
/// - Complexity: O(1).
@swift3_migration(renamed="makeIterator()")
public func generate() -> LazyFilterGenerator<Base.Generator> {
return LazyFilterGenerator(
_base.generate(), whereElementsSatisfy: _predicate)
}
var _base: Base
var _predicate: (Base.Generator.Element) -> Bool
}
extension LazySequenceType {
/// Returns the elements of `self` that satisfy `predicate`.
///
/// - 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.
@warn_unused_result
public func filter(
predicate: (Elements.Generator.Element) -> Bool
) -> LazyFilterSequence<Self.Elements> {
return LazyFilterSequence(
self.elements, whereElementsSatisfy: predicate)
}
}
extension LazyCollectionType {
/// Returns the elements of `self` that satisfy `predicate`.
///
/// - 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.
@warn_unused_result
public func filter(
predicate: (Elements.Generator.Element) -> Bool
) -> LazyFilterCollection<Self.Elements> {
return LazyFilterCollection(
self.elements, whereElementsSatisfy: predicate)
}
}
/// Returns an `Array` containing the elements of `source`,
/// in order, that satisfy the predicate `includeElement`.
@available(*, unavailable, message="call the 'filter()' method on the sequence")
public func filter<S : SequenceType>(
source: S, _ includeElement: (S.Generator.Element) -> Bool
) -> [S.Generator.Element] {
fatalError("unavailable function can't be called")
}
@available(*, unavailable, renamed="FilterSequence")
public struct FilterSequenceView<Base : SequenceType> {}
@available(*, unavailable, renamed="FilterCollectionIndex")
public struct FilterCollectionViewIndex<Base: CollectionType> {}
@available(*, unavailable, renamed="FilterCollection")
public struct FilterCollectionView<Base : CollectionType> {}
// ${'Local Variables'}:
// eval: (read-only-mode 1)
// End: