故障保险withFallback():为什么kotlin编译器无法推断lambda类型? [英] Failsafe withFallback(): why kotlin compiler fails to infer lambda type?

问题描述

我的kotlin代码中包含以下内容:

I have following in my kotlin code:

return Failsafe.with<Boolean>(retryPolicy)
        // Here I want fall back to false
        .withFallback { -> false} // Does not work
        .get { ->
            publish(event)
            true
        }

Kotlin编译器抱怨:

Kotlin compiler complains that:

错误:(89，14)Kotlin:重载分辨率不明确:

Error:(89, 14) Kotlin: Overload resolution ambiguity:

withFallback(p0:(()-> Boolean！)！)的公共最终乐趣:) SyncFailsafe！在net.jodah.failsafe.SyncFailsafe中定义

public final fun withFallback(p0: (() -> Boolean!)!): SyncFailsafe! defined in net.jodah.failsafe.SyncFailsafe

withFallback(p0:(()-> Unit)！)的公共最终乐趣:SyncFailsafe！在net.jodah.failsafe.SyncFailsafe中定义

public final fun withFallback(p0: (() -> Unit)!): SyncFailsafe! defined in net.jodah.failsafe.SyncFailsafe

但是这种方式有效:

val fallback: () -> Boolean = { false }

return Failsafe.with<Boolean>(retryPolicy)
        // Here I want fall back to false
        .withFallback(fallback) // Works
        .get { ->
            publish(event)
            true
        }

有人可以解释一下为什么它不能在括号内使用lambda文字吗?以及如何使其与lambda内联一起工作?

Could somebody explain me why it does not work with lambda literal outside brackets? And how to make it work with lambda inline?

推荐答案

如果您写

val fallback: () -> Unit = { -> false }

您还将看到它也可以编译(它只是丢弃结果).所以 {->false} 可以用于两种类型的()->布尔值和()->单位，编译器不知道您要哪个.

you'll see it compiles as well (it just discards the result). So { -> false} can be used for both types () -> Boolean and () -> Unit and the compiler doesn't know which you want.

要使用lambda，请在此处指定所需的类型:

So to use a lambda, specify the desired type there:

.withFallback({ -> false} as () -> Boolean)

或创建没有过载的扩展功能，例如:

or create an extension function without an overload, e.g.:

fun <T, F> FailsafeConfig<T, F>.withFallbackT(fallback: () -> T) = withFallback(fallback)

return Failsafe.with<Boolean>(retryPolicy)
    .withFallbackT { -> false}...

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