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jasdevjasdev
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Adds Publisher.prefix(while:behavior:). (#70)
* Adds Publisher.prefix(while:behavior:). Figured we should add this to Ext after stumbling upon @jessegrosjean’s [Swift Forums thread](https://forums.swift.org/t/how-to-make-combines-prefix-operator-inclusive/39216) and @mayoff’s [approach with composed operators](https://forums.swift.org/t/how-to-make-combines-prefix-operator-inclusive/39216/8). * Avoid the [PrefixInclusiveEvent] dance.
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‎CombineExt.xcodeproj/project.pbxproj

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@@ -37,6 +37,8 @@
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BF43CC1725008C45005AFA28 /* IgnoreOutputSetOutputTypeTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = BF43CC1625008C45005AFA28 /* IgnoreOutputSetOutputTypeTests.swift */; };
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BFADDC8125BCE4C200465E9B /* FlatMapBatches.swift in Sources */ = {isa = PBXBuildFile; fileRef = BFADDC8025BCE4C200465E9B /* FlatMapBatches.swift */; };
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BFADDC8B25BCE91E00465E9B /* FlatMapBatchesTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = BFADDC8A25BCE91E00465E9B /* FlatMapBatchesTests.swift */; };
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BF45214E259C0C610065E60E /* PrefixWhileBehavior.swift in Sources */ = {isa = PBXBuildFile; fileRef = BF45214D259C0C610065E60E /* PrefixWhileBehavior.swift */; };
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BF452158259C110C0065E60E /* PrefixWhileBehaviorTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = BF452157259C110C0065E60E /* PrefixWhileBehaviorTests.swift */; };
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C387777C24E6BBE900FAD2D8 /* Nwise.swift in Sources */ = {isa = PBXBuildFile; fileRef = C387777B24E6BBE900FAD2D8 /* Nwise.swift */; };
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C387777F24E6BF8F00FAD2D8 /* NwiseTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = C387777D24E6BF6C00FAD2D8 /* NwiseTests.swift */; };
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D836234824EA9446002353AC /* MergeMany.swift in Sources */ = {isa = PBXBuildFile; fileRef = D836234724EA9446002353AC /* MergeMany.swift */; };
@@ -124,6 +126,8 @@
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BF43CC1625008C45005AFA28 /* IgnoreOutputSetOutputTypeTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = IgnoreOutputSetOutputTypeTests.swift; sourceTree = "<group>"; };
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BFADDC8025BCE4C200465E9B /* FlatMapBatches.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FlatMapBatches.swift; sourceTree = "<group>"; };
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BFADDC8A25BCE91E00465E9B /* FlatMapBatchesTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FlatMapBatchesTests.swift; sourceTree = "<group>"; };
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BF45214D259C0C610065E60E /* PrefixWhileBehavior.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PrefixWhileBehavior.swift; sourceTree = "<group>"; };
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BF452157259C110C0065E60E /* PrefixWhileBehaviorTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PrefixWhileBehaviorTests.swift; sourceTree = "<group>"; };
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C387777B24E6BBE900FAD2D8 /* Nwise.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Nwise.swift; sourceTree = "<group>"; };
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C387777D24E6BF6C00FAD2D8 /* NwiseTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NwiseTests.swift; sourceTree = "<group>"; };
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"CombineExt::CombineExt::Product" /* CombineExt.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; path = CombineExt.framework; sourceTree = BUILT_PRODUCTS_DIR; };
@@ -260,6 +264,7 @@
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C387777B24E6BBE900FAD2D8 /* Nwise.swift */,
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OBJ_26 /* Partition.swift */,
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OBJ_27 /* PrefixDuration.swift */,
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BF45214D259C0C610065E60E /* PrefixWhileBehavior.swift */,
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OBJ_28 /* RemoveAllDuplicates.swift */,
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712E36C72711B79000A2AAFE /* RetryWhen.swift */,
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OBJ_29 /* SetOutputType.swift */,
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OBJ_52 /* PartitionTests.swift */,
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OBJ_53 /* PassthroughRelayTests.swift */,
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OBJ_54 /* PrefixDurationTests.swift */,
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BF452157259C110C0065E60E /* PrefixWhileBehaviorTests.swift */,
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OBJ_55 /* RemoveAllDuplicatesTests.swift */,
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OBJ_56 /* ReplaySubjectTests.swift */,
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7182326E26DAAF230026BAD3 /* RetryWhenTests.swift */,
@@ -565,6 +571,7 @@
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D836234A24EA9888002353AC /* MergeManyTests.swift in Sources */,
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OBJ_125 /* CombineLatestManyTests.swift in Sources */,
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BF3D3B67253B88E500D830ED /* IgnoreFailureTests.swift in Sources */,
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BF452158259C110C0065E60E /* PrefixWhileBehaviorTests.swift in Sources */,
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OBJ_126 /* CreateTests.swift in Sources */,
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OBJ_127 /* CurrentValueRelayTests.swift in Sources */,
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C387777F24E6BF8F00FAD2D8 /* NwiseTests.swift in Sources */,
@@ -622,6 +629,7 @@
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OBJ_95 /* RemoveAllDuplicates.swift in Sources */,
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OBJ_96 /* SetOutputType.swift in Sources */,
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OBJ_97 /* ShareReplay.swift in Sources */,
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BF45214E259C0C610065E60E /* PrefixWhileBehavior.swift in Sources */,
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OBJ_98 /* Toggle.swift in Sources */,
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OBJ_99 /* WithLatestFrom.swift in Sources */,
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OBJ_100 /* ZipMany.swift in Sources */,

‎README.md

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@@ -38,7 +38,8 @@ All operators, utilities and helpers respect Combine's publisher contract, inclu
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* [removeAllDuplicates and removeAllDuplicates(by:) ](#removeAllDuplicates)
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* [share(replay:)](#sharereplay)
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* [prefix(duration:tolerance:​on:options:)](#prefixduration)
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* [toggle()](#toggle)
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* [prefix(while:behavior:​)](#prefixwhilebehavior)
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* [toggle()](#toggle)
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* [nwise(_:) and pairwise()](#nwise)
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* [ignoreOutput(setOutputType:)](#ignoreOutputsetOutputType)
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* [ignoreFailure](#ignoreFailure)
@@ -553,7 +554,7 @@ second subscriber: 4
553554

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### prefix(duration:)
555556

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An overload on `Publisher.prefix` that that republishes values for a provided `duration` (in seconds), and then completes.
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An overload on `Publisher.prefix` that republishes values for a provided `duration` (in seconds), and then completes.
557558

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```swift
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let subject = PassthroughSubject<Int, Never>()
@@ -579,6 +580,37 @@ DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
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3
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```
581582

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### prefix(while:behavior:)
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An overload on `Publisher.prefix(while:)` that allows for inclusion of the first element that doesn’t pass the `while` predicate.
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```swift
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let subject = PassthroughSubject<Int, Never>()
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subscription = subject
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.prefix(
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while: { $0 % 2 == 0 },
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behavior: .inclusive
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)
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.sink(
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receivecompletion: { print($0) },
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receiveValue: { print($0) }
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)
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subject.send(0)
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subject.send(2)
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subject.send(4)
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subject.send(5)
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```
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```none
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0
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2
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4
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5
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finished
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```
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### toggle()
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Toggle each boolean element of a publisher collection.

‎Sources/Operators/PrefixWhileBehavior.swift

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1+
//
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// PrefixWhileBehavior.swift
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// CombineExt
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//
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// Created by Jasdev Singh on 29/12/2020.
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// Copyright © 2020 Combine Community. All rights reserved.
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//
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#if canImport(Combine)
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import Combine
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import Foundation
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13+
/// Whether to include the first element that doesn’t pass
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/// the `while` predicate passed to `Combine.Publisher.prefix(while:behavior:)`.
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public enum PrefixWhileBehavior {
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/// Include the first element that doesn’t pass the `while` predicate.
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case inclusive
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/// Exclude the first element that doesn’t pass the `while` predicate.
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case exclusive
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}
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@available(OSX 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
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public extension Publisher {
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/// An overload on `Publisher.prefix(while:)` that allows for inclusion of the first element that doesn’t pass the `while` predicate.
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///
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/// - parameters:
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/// - predicate: A closure that takes an element as its parameter and returns a Boolean value that indicates whether publishing should continue.
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/// - behavior: Whether or not to include the first element that doesn’t pass `predicate`.
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///
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/// - returns: A publisher that passes through elements until the predicate indicates publishing should finish — and optionally that first `predicate`-failing element.
32+
func prefix(
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while predicate: @escaping (Output) -> Bool,
34+
behavior: PrefixWhileBehavior = .exclusive
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) -> AnyPublisher<Output, Failure> {
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switch behavior {
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case .exclusive:
38+
return prefix(while: predicate)
39+
.eraseToAnyPublisher()
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case .inclusive:
41+
return flatMap { next in
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Just(PrefixInclusiveEvent.whileValueOrIncluded(next))
43+
.append(!predicate(next) ? [.end] : [])
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.setFailureType(to: Failure.self)
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}
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.prefix(while: \.isWhileValueOrIncluded)
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.compactMap(\.value)
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.eraseToAnyPublisher()
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}
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}
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}
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#endif
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// MARK: - Helpers
55+
56+
private enum PrefixInclusiveEvent<Output> {
57+
case end
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case whileValueOrIncluded(Output)
59+
60+
var isWhileValueOrIncluded: Bool {
61+
switch self {
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case .end:
63+
return false
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case .whileValueOrIncluded:
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return true
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}
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}
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var value: Output? {
70+
switch self {
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case .end:
72+
return nil
73+
case let .whileValueOrIncluded(inner):
74+
return inner
75+
}
76+
}
77+
}

‎Tests/PrefixWhileBehaviorTests.swift

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1+
//
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// PrefixWhileBehaviorTests.swift
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// CombineExt
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//
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// Created by Jasdev Singh on 29/12/2020.
6+
// Copyright © 2020 Combine Community. All rights reserved.
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//
8+
9+
#if !os(watchOS)
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import Combine
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import CombineExt
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import XCTest
13+
14+
@available(OSX 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
15+
final class PrefixWhileBehaviorTests: XCTestCase {
16+
private struct SomeError: Error, Equatable {}
17+
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private var cancellable: AnyCancellable!
19+
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func testExclusiveValueEventsWithFinished() {
21+
let intSubject = PassthroughSubject<Int, Never>()
22+
23+
var values = [Int]()
24+
var completions = [Subscribers.Completion<Never>]()
25+
26+
cancellable = intSubject
27+
.prefix(
28+
while: { $0 % 2 == 0 },
29+
behavior: .exclusive
30+
)
31+
.sink(
32+
receiveCompletion: { completions.append($0) },
33+
receiveValue: { values.append($0) }
34+
)
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[0, 2, 4, 5]
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.forEach(intSubject.send)
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XCTAssertEqual(values, [0, 2, 4])
40+
XCTAssertEqual(completions, [.finished])
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}
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func testExclusiveValueEventsWithError() {
44+
let intSubject = PassthroughSubject<Int, SomeError>()
45+
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var values = [Int]()
47+
var completions = [Subscribers.Completion<SomeError>]()
48+
49+
cancellable = intSubject
50+
.prefix(
51+
while: { $0 % 2 == 0 },
52+
behavior: .exclusive
53+
)
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.sink(
55+
receiveCompletion: { completions.append($0) },
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receiveValue: { values.append($0) }
57+
)
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[0, 2, 4]
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.forEach(intSubject.send)
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intSubject.send(completion: .failure(.init()))
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XCTAssertEqual(values, [0, 2, 4])
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XCTAssertEqual(completions, [.failure(.init())])
66+
}
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func testInclusiveValueEventsWithStopElement() {
69+
let intSubject = PassthroughSubject<Int, Never>()
70+
71+
var values = [Int]()
72+
var completions = [Subscribers.Completion<Never>]()
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cancellable = intSubject
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.prefix(
76+
while: { $0 % 2 == 0 },
77+
behavior: .inclusive
78+
)
79+
.sink(
80+
receiveCompletion: { completions.append($0) },
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receiveValue: { values.append($0) }
82+
)
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[0, 2, 4, 5]
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.forEach(intSubject.send)
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XCTAssertEqual(values, [0, 2, 4, 5])
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XCTAssertEqual(completions, [.finished])
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}
90+
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func testInclusiveValueEventsWithErrorAfterStopElement() {
92+
let intSubject = PassthroughSubject<Int, SomeError>()
93+
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var values = [Int]()
95+
var completions = [Subscribers.Completion<SomeError>]()
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cancellable = intSubject
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.prefix(
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while: { $0 % 2 == 0 },
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behavior: .inclusive
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)
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.sink(
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receiveCompletion: { completions.append($0) },
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receiveValue: { values.append($0) }
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)
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[0, 2, 4, 5]
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.forEach(intSubject.send)
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intSubject.send(completion: .failure(.init()))
111+
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XCTAssertEqual(values, [0, 2, 4, 5])
113+
XCTAssertEqual(completions, [.finished])
114+
}
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func testInclusiveValueEventsWithErrorBeforeStop() {
117+
let intSubject = PassthroughSubject<Int, SomeError>()
118+
119+
var values = [Int]()
120+
var completions = [Subscribers.Completion<SomeError>]()
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122+
cancellable = intSubject
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.prefix(
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while: { $0 % 2 == 0 },
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behavior: .inclusive
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)
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.sink(
128+
receiveCompletion: { completions.append($0) },
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receiveValue: { values.append($0) }
130+
)
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[0, 2, 4]
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.forEach(intSubject.send)
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intSubject.send(completion: .failure(.init()))
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XCTAssertEqual(values, [0, 2, 4])
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XCTAssertEqual(completions, [.failure(.init())])
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}
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func testInclusiveEarlyCompletion() {
142+
let intSubject = PassthroughSubject<Int, SomeError>()
143+
144+
var values = [Int]()
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var completions = [Subscribers.Completion<SomeError>]()
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cancellable = intSubject
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.prefix(
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while: { $0 % 2 == 0 },
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behavior: .inclusive
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)
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.sink(
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receiveCompletion: { completions.append($0) },
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receiveValue: { values.append($0) }
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)
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[0, 2, 4]
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.forEach(intSubject.send)
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intSubject.send(completion: .finished)
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XCTAssertEqual(values, [0, 2, 4])
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XCTAssertEqual(completions, [.finished])
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}
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}
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#endif

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