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//===--- FlatMap.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
//
//===----------------------------------------------------------------------===//
extension LazySequenceProtocol {
/// Returns the concatenated results of mapping the given transformation over
/// this sequence.
///
/// Use this method to receive a single-level sequence when your
/// transformation produces a sequence or collection for each element.
/// Calling `flatMap(_:)` on a sequence `s` is equivalent to calling
/// `s.map(transform).joined()`.
///
/// - Complexity: O(1)
@inlinable // lazy-performance
public func flatMap<SegmentOfResult>(
_ transform: @escaping (Elements.Element) -> SegmentOfResult
) -> LazySequence<
FlattenSequence<LazyMapSequence<Elements, SegmentOfResult>>> {
return self.map(transform).joined()
}
/// Returns the non-`nil` results of mapping the given transformation over
/// this sequence.
///
/// Use this method to receive a sequence of non-optional values when your
/// transformation produces an optional value.
///
/// - Parameter transform: A closure that accepts an element of this sequence
/// as its argument and returns an optional value.
///
/// - Complexity: O(1)
@inlinable // lazy-performance
public func compactMap<ElementOfResult>(
_ transform: @escaping (Elements.Element) -> ElementOfResult?
) -> LazyMapSequence<
LazyFilterSequence<
LazyMapSequence<Elements, ElementOfResult?>>,
ElementOfResult
> {
return self.map(transform).filter { $0 != nil }.map { $0! }
}
}
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