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jasdev
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freak4pc
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Subs in a composed form of withLatestFrom and adds test cases for lone upstream completions.
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‎Sources/Operators/WithLatestFrom.swift

+95-211
Original file line numberDiff line numberDiff line change
@@ -12,227 +12,111 @@ import Combine
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// MARK: - Operator methods
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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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/// Merges two publishers into a single publisher by combining each value
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/// from self with the latest value from the second publisher, if any.
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///
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/// - parameter other: A second publisher source.
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/// - parameter resultSelector: Function to invoke for each value from the self combined
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/// with the latest value from the second source, if any.
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///
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/// - returns: A publisher containing the result of combining each value of the self
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/// with the latest value from the second publisher, if any, using the
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/// specified result selector function.
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func withLatestFrom<Other: Publisher, Result>(_ other: Other,
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resultSelector: @escaping (Output, Other.Output) -> Result)
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-> Publishers.WithLatestFrom<Self, Other, Result> {
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return .init(upstream: self, second: other, resultSelector: resultSelector)
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}
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/// Merges three publishers into a single publisher by combining each value
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/// from self with the latest value from the second and third publisher, if any.
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///
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/// - parameter other: A second publisher source.
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/// - parameter other1: A third publisher source.
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/// - parameter resultSelector: Function to invoke for each value from the self combined
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/// with the latest value from the second and third source, if any.
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///
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/// - returns: A publisher containing the result of combining each value of the self
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/// with the latest value from the second and third publisher, if any, using the
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/// specified result selector function.
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func withLatestFrom<Other: Publisher, Other1: Publisher, Result>(_ other: Other,
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_ other1: Other1,
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resultSelector: @escaping (Output, (Other.Output, Other1.Output)) -> Result)
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-> Publishers.WithLatestFrom<Self, AnyPublisher<(Other.Output, Other1.Output), Self.Failure>, Result>
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where Other.Failure == Failure, Other1.Failure == Failure {
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let combined = other.combineLatest(other1)
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.eraseToAnyPublisher()
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return .init(upstream: self, second: combined, resultSelector: resultSelector)
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}
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/// Merges four publishers into a single publisher by combining each value
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/// from self with the latest value from the second, third and fourth publisher, if any.
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///
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/// - parameter other: A second publisher source.
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/// - parameter other1: A third publisher source.
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/// - parameter other2: A fourth publisher source.
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/// - parameter resultSelector: Function to invoke for each value from the self combined
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/// with the latest value from the second, third and fourth source, if any.
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///
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/// - returns: A publisher containing the result of combining each value of the self
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/// with the latest value from the second, third and fourth publisher, if any, using the
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/// specified result selector function.
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func withLatestFrom<Other: Publisher, Other1: Publisher, Other2: Publisher, Result>(_ other: Other,
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_ other1: Other1,
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_ other2: Other2,
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resultSelector: @escaping (Output, (Other.Output, Other1.Output, Other2.Output)) -> Result)
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-> Publishers.WithLatestFrom<Self, AnyPublisher<(Other.Output, Other1.Output, Other2.Output), Self.Failure>, Result>
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where Other.Failure == Failure, Other1.Failure == Failure, Other2.Failure == Failure {
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let combined = other.combineLatest(other1, other2)
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.eraseToAnyPublisher()
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return .init(upstream: self, second: combined, resultSelector: resultSelector)
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}
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/// Upon an emission from self, emit the latest value from the
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/// second publisher, if any exists.
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///
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/// - parameter other: A second publisher source.
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///
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/// - returns: A publisher containing the latest value from the second publisher, if any.
81-
func withLatestFrom<Other: Publisher>(_ other: Other)
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-> Publishers.WithLatestFrom<Self, Other, Other.Output> {
83-
return .init(upstream: self, second: other) { $1 }
84-
}
85-
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/// Upon an emission from self, emit the latest value from the
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/// second and third publisher, if any exists.
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///
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/// - parameter other: A second publisher source.
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/// - parameter other1: A third publisher source.
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///
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/// - returns: A publisher containing the latest value from the second and third publisher, if any.
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func withLatestFrom<Other: Publisher, Other1: Publisher>(_ other: Other,
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_ other1: Other1)
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-> Publishers.WithLatestFrom<Self, AnyPublisher<(Other.Output, Other1.Output), Self.Failure>, (Other.Output, Other1.Output)>
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where Other.Failure == Failure, Other1.Failure == Failure {
97-
withLatestFrom(other, other1) { $1 }
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}
99-
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/// Upon an emission from self, emit the latest value from the
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/// second, third and forth publisher, if any exists.
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///
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/// - parameter other: A second publisher source.
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/// - parameter other1: A third publisher source.
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/// - parameter other2: A forth publisher source.
106-
///
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/// - returns: A publisher containing the latest value from the second, third and forth publisher, if any.
108-
func withLatestFrom<Other: Publisher, Other1: Publisher, Other2: Publisher>(_ other: Other,
109-
_ other1: Other1,
110-
_ other2: Other2)
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-> Publishers.WithLatestFrom<Self, AnyPublisher<(Other.Output, Other1.Output, Other2.Output), Self.Failure>, (Other.Output, Other1.Output, Other2.Output)>
112-
where Other.Failure == Failure, Other1.Failure == Failure, Other2.Failure == Failure {
113-
withLatestFrom(other, other1, other2) { $1 }
114-
}
115-
}
116-
117-
// MARK: - Publisher
118-
@available(OSX 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
119-
public extension Publishers {
120-
struct WithLatestFrom<Upstream: Publisher,
121-
Other: Publisher,
122-
Output>: Publisher where Upstream.Failure == Other.Failure {
123-
public typealias Failure = Upstream.Failure
124-
public typealias ResultSelector = (Upstream.Output, Other.Output) -> Output
125-
126-
private let upstream: Upstream
127-
private let second: Other
128-
private let resultSelector: ResultSelector
129-
private var latestValue: Other.Output?
130-
131-
init(upstream: Upstream,
132-
second: Other,
133-
resultSelector: @escaping ResultSelector) {
134-
self.upstream = upstream
135-
self.second = second
136-
self.resultSelector = resultSelector
137-
}
138-
139-
public func receive<S: Subscriber>(subscriber: S) where Failure == S.Failure, Output == S.Input {
140-
subscriber.receive(subscription: Subscription(upstream: upstream,
141-
downstream: subscriber,
142-
second: second,
143-
resultSelector: resultSelector))
15+
/// Merges two publishers into a single publisher by combining each value
16+
/// from self with the latest value from the second publisher, if any.
17+
///
18+
/// - parameter other: A second publisher source.
19+
/// - parameter resultSelector: Function to invoke for each value from the self combined
20+
/// with the latest value from the second source, if any.
21+
///
22+
/// - returns: A publisher containing the result of combining each value of the self
23+
/// with the latest value from the second publisher, if any, using the
24+
/// specified result selector function.
25+
func withLatestFrom<Other: Publisher, Result>(_ other: Other,
26+
resultSelector: @escaping (Output, Other.Output) -> Result)
27+
-> AnyPublisher<Result, Failure>
28+
where Other.Failure == Failure {
29+
let upstream = share()
30+
31+
return other
32+
.map { second in upstream.map { resultSelector($0, second) } }
33+
.switchToLatest()
34+
.zip(upstream) // `zip`ping and discarding `\.1` allows for
35+
// upstream completions to be projected down immediately.
36+
.map(\.0)
37+
.eraseToAnyPublisher()
14438
}
145-
}
146-
}
14739

148-
// MARK: - Subscription
149-
@available(OSX 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
150-
private extension Publishers.WithLatestFrom {
151-
class Subscription<Downstream: Subscriber>: Combine.Subscription, CustomStringConvertible where Downstream.Input == Output, Downstream.Failure == Failure {
152-
private let resultSelector: ResultSelector
153-
private var sink: Sink<Upstream, Downstream>?
154-
155-
private let upstream: Upstream
156-
private let downstream: Downstream
157-
private let second: Other
158-
159-
// Secondary (other) publisher
160-
private var latestValue: Other.Output?
161-
private var otherSubscription: Cancellable?
162-
private var preInitialDemand = Subscribers.Demand.none
163-
164-
init(upstream: Upstream,
165-
downstream: Downstream,
166-
second: Other,
167-
resultSelector: @escaping ResultSelector) {
168-
self.upstream = upstream
169-
self.second = second
170-
self.downstream = downstream
171-
self.resultSelector = resultSelector
172-
173-
trackLatestFromSecond { [weak self] in
174-
guard let self = self else { return }
175-
self.request(self.preInitialDemand)
176-
self.preInitialDemand = .none
177-
}
40+
/// Merges three publishers into a single publisher by combining each value
41+
/// from self with the latest value from the second and third publisher, if any.
42+
///
43+
/// - parameter other: A second publisher source.
44+
/// - parameter other1: A third publisher source.
45+
/// - parameter resultSelector: Function to invoke for each value from the self combined
46+
/// with the latest value from the second and third source, if any.
47+
///
48+
/// - returns: A publisher containing the result of combining each value of the self
49+
/// with the latest value from the second and third publisher, if any, using the
50+
/// specified result selector function.
51+
func withLatestFrom<Other: Publisher, Other1: Publisher, Result>(_ other: Other,
52+
_ other1: Other1,
53+
resultSelector: @escaping (Output, (Other.Output, Other1.Output)) -> Result)
54+
-> AnyPublisher<Result, Failure>
55+
where Other.Failure == Failure, Other1.Failure == Failure {
56+
withLatestFrom(other.combineLatest(other1), resultSelector: resultSelector)
17857
}
17958

180-
func request(_ demand: Subscribers.Demand) {
181-
guard latestValue != nil else {
182-
preInitialDemand += demand
183-
return
184-
}
185-
186-
self.sink?.demand(demand)
59+
/// Merges four publishers into a single publisher by combining each value
60+
/// from self with the latest value from the second, third and fourth publisher, if any.
61+
///
62+
/// - parameter other: A second publisher source.
63+
/// - parameter other1: A third publisher source.
64+
/// - parameter other2: A fourth publisher source.
65+
/// - parameter resultSelector: Function to invoke for each value from the self combined
66+
/// with the latest value from the second, third and fourth source, if any.
67+
///
68+
/// - returns: A publisher containing the result of combining each value of the self
69+
/// with the latest value from the second, third and fourth publisher, if any, using the
70+
/// specified result selector function.
71+
func withLatestFrom<Other: Publisher, Other1: Publisher, Other2: Publisher, Result>(_ other: Other,
72+
_ other1: Other1,
73+
_ other2: Other2,
74+
resultSelector: @escaping (Output, (Other.Output, Other1.Output, Other2.Output)) -> Result)
75+
-> AnyPublisher<Result, Failure>
76+
where Other.Failure == Failure, Other1.Failure == Failure, Other2.Failure == Failure {
77+
withLatestFrom(other.combineLatest(other1, other2), resultSelector: resultSelector)
18778
}
18879

189-
// Create an internal subscription to the `Other` publisher,
190-
// constantly tracking its latest value
191-
private func trackLatestFromSecond(onInitialValue: @escaping () -> Void) {
192-
var gotInitialValue = false
193-
194-
let subscriber = AnySubscriber<Other.Output, Other.Failure>(
195-
receiveSubscription: { [weak self] subscription in
196-
self?.otherSubscription = subscription
197-
subscription.request(.unlimited)
198-
},
199-
receiveValue: { [weak self] value in
200-
guard let self = self else { return .none }
201-
self.latestValue = value
202-
203-
if !gotInitialValue {
204-
// When getting initial value, start pulling values
205-
// from upstream in the main sink
206-
self.sink = Sink(upstream: self.upstream,
207-
downstream: self.downstream,
208-
transformOutput: { [weak self] value in
209-
guard let self = self,
210-
let other = self.latestValue else { return nil }
211-
212-
return self.resultSelector(value, other)
213-
},
214-
transformFailure: { $0 })
215-
216-
// Signal initial value to start fulfilling downstream demand
217-
gotInitialValue = true
218-
onInitialValue()
219-
}
220-
221-
return .unlimited
222-
},
223-
receiveCompletion: nil)
224-
225-
self.second.subscribe(subscriber)
80+
/// Upon an emission from self, emit the latest value from the
81+
/// second publisher, if any exists.
82+
///
83+
/// - parameter other: A second publisher source.
84+
///
85+
/// - returns: A publisher containing the latest value from the second publisher, if any.
86+
func withLatestFrom<Other: Publisher>(_ other: Other)
87+
-> AnyPublisher<Other.Output, Failure>
88+
where Other.Failure == Failure {
89+
withLatestFrom(other) { $1 }
22690
}
22791

228-
var description: String {
229-
return "WithLatestFrom.Subscription<\(Output.self), \(Failure.self)>"
92+
/// Upon an emission from self, emit the latest value from the
93+
/// second and third publisher, if any exists.
94+
///
95+
/// - parameter other: A second publisher source.
96+
/// - parameter other1: A third publisher source.
97+
///
98+
/// - returns: A publisher containing the latest value from the second and third publisher, if any.
99+
func withLatestFrom<Other: Publisher, Other1: Publisher>(_ other: Other,
100+
_ other1: Other1)
101+
-> AnyPublisher<(Other.Output, Other1.Output), Failure>
102+
where Other.Failure == Failure, Other1.Failure == Failure {
103+
withLatestFrom(other, other1) { $1 }
230104
}
231105

232-
func cancel() {
233-
sink = nil
234-
otherSubscription?.cancel()
106+
/// Upon an emission from self, emit the latest value from the
107+
/// second, third and forth publisher, if any exists.
108+
///
109+
/// - parameter other: A second publisher source.
110+
/// - parameter other1: A third publisher source.
111+
/// - parameter other2: A forth publisher source.
112+
///
113+
/// - returns: A publisher containing the latest value from the second, third and forth publisher, if any.
114+
func withLatestFrom<Other: Publisher, Other1: Publisher, Other2: Publisher>(_ other: Other,
115+
_ other1: Other1,
116+
_ other2: Other2)
117+
-> AnyPublisher<(Other.Output, Other1.Output, Other2.Output), Failure>
118+
where Other.Failure == Failure, Other1.Failure == Failure, Other2.Failure == Failure {
119+
withLatestFrom(other, other1, other2) { $1 }
235120
}
236-
}
237121
}
238122
#endif

‎Tests/WithLatestFromTests.swift

+51
Original file line numberDiff line numberDiff line change
@@ -386,5 +386,56 @@ class WithLatestFromTests: XCTestCase {
386386
subject1.send(completion: .finished)
387387
XCTAssertTrue(completed)
388388
}
389+
390+
func testWithLatestFromCompletion() {
391+
let subject1 = PassthroughSubject<Int, Never>()
392+
let subject2 = PassthroughSubject<String, Never>()
393+
var results = [String]()
394+
var completed = false
395+
396+
subscription = subject1
397+
.withLatestFrom(subject2)
398+
.sink(receiveCompletion: { _ in completed = true },
399+
receiveValue: { results.append($0) })
400+
401+
subject1.send(completion: .finished)
402+
XCTAssertTrue(completed)
403+
XCTAssertTrue(results.isEmpty)
404+
}
405+
406+
func testWithLatestFrom2Completion() {
407+
let subject1 = PassthroughSubject<Int, Never>()
408+
let subject2 = PassthroughSubject<String, Never>()
409+
let subject3 = PassthroughSubject<String, Never>()
410+
var results = [(String, String)]()
411+
var completed = false
412+
413+
subscription = subject1
414+
.withLatestFrom(subject2, subject3)
415+
.sink(receiveCompletion: { _ in completed = true },
416+
receiveValue: { results.append($0) })
417+
418+
subject1.send(completion: .finished)
419+
XCTAssertTrue(completed)
420+
XCTAssertTrue(results.isEmpty)
421+
}
422+
423+
func testWithLatestFrom3Completion() {
424+
let subject1 = PassthroughSubject<Int, Never>()
425+
let subject2 = PassthroughSubject<String, Never>()
426+
let subject3 = PassthroughSubject<String, Never>()
427+
let subject4 = PassthroughSubject<String, Never>()
428+
var results = [(String, String, String)]()
429+
var completed = false
430+
431+
subscription = subject1
432+
.withLatestFrom(subject2, subject3, subject4)
433+
.sink(receiveCompletion: { _ in completed = true },
434+
receiveValue: { results.append($0) })
435+
436+
subject1.send(completion: .finished)
437+
XCTAssertTrue(completed)
438+
XCTAssertTrue(results.isEmpty)
439+
}
389440
}
390441
#endif

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