Kotlin:使用地图变换时{}和()之间的区别? [英] Kotlin: Difference between {} and () while using map transform?

问题描述

我是Kotlin的新手. Ive始终使用带有花括号的map转换.然后-

I'm new to kotlin. Ive always used the map transform with curly braces. Then -

为什么这样做->

val x = someList.map(::SomeConstructor)

这不是吗?

val x = someList.map{ ::SomeConstructor }

在在线教程的任何地方，我都没有发现带有圆括号的地图的用法.

I didn't find usage of map with circular brackets anywhere on the online tutorials.

请尝试详细解释，或提供合适的参考文章.

Please try to explain in detail, or provide suitable reference article.

推荐答案

如果并且仅当函数的最后一个参数是lambda时，您可以将其从调用括号中提取出来，以使其内联在函数的右侧.它允许使用更好的DSL语法.

If and only if the last argument of a function is a lambda, you can extract it from the call paranthesis, to put it inline on the right of the function. It allows a nicer DSL syntax.

编辑:让我们举个例子:

一个很好的用例是上下文编程.假设您有一个可关闭的物体.您想划定它的用法，以确保不再需要它时可以正确关闭它.在Java中，您可以获得try-with-resources:

One of the good use-case is context programming. Imagine you've got a closeable object. You want to delimit its usage to ensure it's properly closed once not needed anymore. In Java, you've got the try-with-resources:

try (final AutoCloseable myResource = aquireStuff()) {
  // use your resource here.
}

科特琳提供use功能.现在，您可以执行以下任一操作:

Kotlin provide the use function. Now, you can do either :

acquireStuff().use( { doStuff1(it) ; doStuff2(it) } )

或写:

acquireStuff().use {
  doStuff1(it)
  doStuff2(it)
}

它看起来像Java try-w-resource，但是可以扩展到您的任何API.允许您设计向最终用户提供高级构造的库.

It looks like a Java try-w-resource, but is extensible to any of your API. Allowing you to design libraries giving advanced constructs to end-users.

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