Kotlin:"return @"是什么意思?意思是?

Kotlin:

问题描述：

我在我的一个项目中使用RxJava，我使用Android Studio插件将我的一个类转换为Kotlin，并在map flatMap lambda(java中的Func1)之一中，中间体返回如下:.

I'm using RxJava in one of my projects, I converted one of my classes to Kotlin using the Android Studio plugin and in one of map flatMap lambda (Func1 in java), intermediates returns looks like the following @Func1.

我不知道这意味着什么.

I have no idea what this means.

something.flatMap(Func1<ArticleCriteria, Observable<Pair<String, String>>> {
    val isTemporaryClone = it.isATemporaryClone
    val isTheOriginalToken = it.tokenIsOriginalHere

    if (isTemporaryClone) {
        if (!isTheOriginalToken) {
            return@Func1 paramsError("Token is always original for temp articles")
        }

        return@Func1 mJobRunner.doNotRun(DeleteArticleJob.TAG)
                            .doOnNext(deletePersonalActionById(articleId))
    }

    runArticleJobAsync(DeleteArticleJob.TAG, it)
})

答

在Kotlin中，

In Kotlin, the return@label syntax is used for specifying which function among several nested ones this statement returns from.

它与函数文字(lambda)和局部函数一起使用.未标记的return语句从封闭的fun的最近(即最里面)返回(忽略lambda).考虑一下此功能:

It works with function literals (lambdas) and local functions. Non-labeled return statements return from the nearest (i.e. innermost) enclosing fun (ignoring lambdas). Consider this function:

fun foo(ints: List<Int>) {
    ints.forEach {
        if (it == 0) return
        print(it)
    }
}

^{在这里，return将完成foo的执行，而不仅仅是lambda.}

^{Here, return will finish the execution of foo, not just the lambda.}

但是，如果要从其他任何函数(lambda或外部fun)返回，则必须在return语句中将其指定为标签:

But if you want to return from any other function (a lambda or an outer fun) you have to specify it as a label at return statement:

fun foo(ints: List<Int>) {
    ints.forEach {
        if (it == 0) return@forEach // implicit label for lambda passed to forEach
        print(it)
    }
}

fun foo(ints: List<Int>): List<String> {
    val result = ints.map f@{
        if (it == 0) return@f "zero" // return at named label
        if (it == -1) return emptyList() // return at foo
        "number $it" // expression returned from lambda
    }
    return result
}

foo(listOf(1, -1, 1)) // []
foo(listOf(1, 0, 1)) // ["number 1", "zero", "number 1"]

非本地退货(即从外部函数)仅支持 local 和内联函数，因为如果未内联lambda(或将函数放置在对象内部) ，因此不能保证仅在封闭函数内部调用它(例如，可以将其存储在变量中，然后再调用)，在这种情况下，非本地返回将毫无意义.

Non-local return (i.e. return from outer functions) from a lambda is only supported for local and inline functions, because if a lambda is not inlined (or a function is placed inside an object), it is not guaranteed to be called only inside the enclosing function (e.g. it can be stored in a variable and called later), and the non-local return would make no sense in this case.

合格的this 也有类似的语法，用于引用外部示波器的接收器:this@outer.

Kotlin:"return @"是什么意思?意思是?

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