Operator之数据合并(Mixing elements from multiple publishers)
combineLatest/CombineLatest3/CombineLatest4
combineLatest把2个publisher的数据进行合并，正常情况下，2个publisher中任何一个产生新的数据，就会把数据合并后输出，遇到错误pipline立刻终止。
合并2个publisher
输出的数据为元组
var cancellables = Set<AnyCancellable>()
let firstPublisher = PassthroughSubject<Int, MyCustomError>()
let secondPublisher = PassthroughSubject<String, MyCustomError>()
firstPublisher
.combineLatest(secondPublisher)
.sink(receiveCompletion: { completion in
print("结束了")
switch completion {
case .finished:
print("完成")
case .failure(let error):
print("错误：\(error.localizedDescription)")
}
}, receiveValue: { someValue in
print("someValue: \(someValue)")
})
.store(in: &cancellables)
firstPublisher.send(1)
secondPublisher.send("a")
firstPublisher.send(2)
打印结果：
someValue: (1, "a")
someValue: (2, "a")
merge/merge3/merge4/merge5/merge6/merge7/merge8/MergeMany
merge用于合并2-8个publisers的数据成一个publisher，combineLatest会把每个publiser的latest数据组合成一个元组，而merge只要接受到新数据就输出。
MergeMany用于合并多个publisers，写法都一样，参考combineLatest即可
zip/zip3/zip4
zip和combineLatest非常相似，默认情况下会返回成组的数据，但他们最大的不同在于zip不会使用latest值，它使用的是新值。
var cancellables = Set<AnyCancellable>()
let pub1 = PassthroughSubject<Int, Never>()
let pub2 = PassthroughSubject<Int, Never>()
pub1
.zip(pub2)
.sink(receiveCompletion: { completion in
print("结束了")
switch completion {
case .finished:
print("完成")
case .failure(let error):
print("错误：\(error.localizedDescription)")
}
}, receiveValue: { someValue in
print("someValue: \(someValue)")
})
.store(in: &cancellables)
pub1.send(1)
pub1.send(2)
pub1.send(3)
pub2.send(4)
pub2.send(5)
使用.zip返回的是(1,4)和(2,5)
而使用.combineLatest返回的则是(3,4)和(3,5)