Rx scan()，无法从种子和另一个可观察对象生成可观察对象 [英] Rx scan(), cannot generate observable from seed and another observable

问题描述

我有一个种子值 Triangle (Bool) 和一个发出值 Circle (Int) 的 observable.我的目的是在每次从该 observable 发出一个值时生成一个新的 observable (Triangle, Circle)，将 Triangle 值转换为否定当前值.这是我的大理石图:

I have a seed value Triangle (Bool) and an observable that emits values Circle (Int). My intention is to generate a new observable (Triangle, Circle) each time a value is emitted from that observable, transforming the Triangle value negating the current value. This is my marble diagram:

但是我无法实现它，我不知道scan 是否是正确的操作符.这是我的代码:

But I cannot achieve it, and I don't know if scan is the correct operator. This is my code:

typealias Triangle = Bool
typealias Circle = Int

func scan() {
    let triangle: Triangle = false
    circleObservable
        .scan(triangle, accumulator: ({ (triangle, circle) -> (Triangle, Circle) in
            return (!triangle, circle)
        }))
}

这会产生编译器错误:

无法转换类型 '(Triangle, Circle) -> (Triangle,Circle)'(又名 '(Bool, Int) -> (Bool, Int)')到预期的参数类型'(_, _) -> _'

Cannot convert value of type '(Triangle, Circle) -> (Triangle, Circle)' (aka '(Bool, Int) -> (Bool, Int)') to expected argument type '(_, _) -> _'

谢谢！

推荐答案

circleObservable.scan((Triangle(false), Circle()), accumulator: { lastValue, circle -> (Triangle, Circle) in (!lastValue.0, circle) })

或者更简单:

typealias Triangle = Bool
typealias Circle = Int

func scan(circle: Observable<Circle>) -> Observable<(Triangle, Circle)> {
    return circle.scan((Triangle(false), Circle())) { (!$0.0, $1) }
}

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