Map
Projects each element of an observable sequence into a new form.
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public func map<Result>(_ transform: @escaping (Element) throws -> Result)
-> Observable<Result> {
return Map(source: self.asObservable(), transform: transform)
}
final private class MapSink<SourceType, Observer: ObserverType>: Sink, ObserverType
中间订阅层，用于中间处理，产生最终结果，输出给最终Observer
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typealias ResultType = Observer.Element
typealias Transform = (SourceType) throws -> ResultType
private let _transform: Transform
func on(_ event: Event<SourceType>) {
switch event {
case .next(let element):
do {
let mappedElement = try self._transform(element)
self.forwardOn(.next(mappedElement))
}
catch let e {
self.forwardOn(.error(e))
self.dispose()
}
case .error(let error):
self.forwardOn(.error(error))
self.dispose()
case .completed:
self.forwardOn(.completed)
self.dispose()
}
}
final private class Map<SourceType, ResultType>: Producer
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typealias Transform = (SourceType) throws -> ResultType
private let _source: Observable<SourceType>
private let _transform: Transform
override func run<Observer: ObserverType>(_ observer: Observer, cancel: Cancelable) -> (sink: Disposable, subscription: Disposable) where Observer.Element == ResultType {
let sink = MapSink(transform: self._transform, observer: observer, cancel: cancel)
let subscription = self._source.subscribe(sink)
return (sink: sink, subscription: subscription)
}