[英]Kotlin - forEach
I am beginner in Kotlin. 我是科特林的初学者。 How do you explain the following code snippet ?
您如何解释以下代码片段?
fun main(args: Array<String>) {
var k = listOf<Double>(1.2,77.8,6.3,988.88,0.1)
k.forEach(::println)
}
This runs fine and gives the list but can someone please help with the explanation for how does k.forEach(::println) really work? 这样可以很好地运行并给出列表,但是有人可以帮忙解释一下k.forEach(:: println)实际如何工作吗?
forEach
takes each element in k
and does what you specify it to do. forEach
发生在每个元素k
并没有指定它做什么 。 In your example, the " what " argument is ::println
, which refers to the stdlib function println(message: Any)
. 在您的示例中,“ what ”参数是
::println
,它表示stdlib函数println(message: Any)
。 The ::
introduced a function reference to this function. ::
引入了对此函数的函数引用 。 Each element is passed as the argument message
to println
and thus it's being printed on the console. 每个元素都作为参数
message
给println
,因此将其打印在控制台上。
To make it more clear, you could pass a lambda instead of the function reference like this: 为了更加清楚,您可以传递lambda而不是像这样的函数引用:
k.forEach{
println(it)
}
inline fun Iterable.forEach(action: (T) -> Unit) 内联乐趣Iterable.forEach(action:(T)-> Unit)
public inline fun Iterable.forEach(action: (T) -> Unit): Unit { for (element in this) action(element) }
public inline fun Iterable.forEach(action:(T)-> Unit):Unit {代表(此元素)action(element)}
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