swift - 如何扩展ReactiveCocoa4的SignalProducerType

Question

我尝试使用 SequenceType 值扩展 SignalProducerType。但我做不到。编译时出现“表达式类型不明确，没有更多上下文”错误。

protocol TranslatorType {
    typealias Source
    typealias Destination
    func translate(source: Source) -> Destination
}

extension SignalProducerType where Value: SequenceType {
    func translate<T: TranslatorType, U: SequenceType where T.Source == Value.Generator.Element, T.Destination == U.Generator.Element>(translator: T) -> ReactiveCocoa.SignalProducer<U, Error> {
        return lift { $0.map { seq in seq.map(translator.translate) } } # Type of expression is ambiguous without more context error
    }
}

我怎样才能做到这一点？

Answer 1

SequenceType 的 map 函数返回一个数组，您无法映射到通用 SequenceType。将类型 U 改为数组，即可编译:

extension SignalProducerType where Value: SequenceType {
    func translate<T: TranslatorType, V where T.Source == Value.Generator.Element, T.Destination == V>(translator: T) -> ReactiveCocoa.SignalProducer<[V], Error> {
        return lift {  $0.map { seq in seq.map(translator.translate) } }
    }
}