.()在 Kotlin 中是什么意思

发布于06月08日

我见过函数具有由ClassName.()指定的参数的示例这似乎不是扩展函数，它是ClassName.Function()

private val View.viewFinder: View.(Int) -> View?
    get() = { findViewById(it) }

Which I don't quite know the function of,

还有MaterialDrawerKt

fun Activity.drawer(setup: DrawerBuilderKt.() -> Unit = {}): Drawer {
    val builder = DrawerBuilderKt(this)
    builder.setup()
    return builder.build()
}

Where the code allows you to directly call

drawer {
    ...
}

rather than give it arguments surrounded by the parentheses.

有关于这个的文件吗？

推荐答案

A function that takes in nothing and returns nothing in Kotlin looks like:

var function : () -> Unit

The difference is that the function in your code takes in nothing, returns nothing, but is invoked on an object.

例如

class Builder (val multiplier: Int) {

    fun invokeStuff(action: (Builder.() -> Unit)) {
        this.action()
    }

    fun multiply(value: Int) : Int {
        return value * multiplier
    }
}

这里重要的一点是我们宣布"行动"类型的方式