Kotlin:使用lambda代替功能界面? [英] Kotlin: Use a lambda in place of a functional interface?
问题描述
在Java中我们可以这样做
Events.handler(Handshake.class,hs - > out.println(hs));
In Java we can do this
Events.handler(Handshake.class, hs -> out.println(hs));
在Kotlin中,我试图复制行为来取代它:
In Kotlin however I am trying to replicate the behavior to replace this:
Events.handler(Handshake::class, object : EventHandler<Handshake> {
override fun handle(event: Handshake) {
println(event.sent)
}
})
更方便:
Events.handler(Handshake :: class,EventHandler< Handshake> {println(it.sent)})
对于某些人参考 EventHandler的原因
:
更优选的是,我想使用更短的东西:
Events.handler(Handshake :: class,{println(it.sent) )})
More preferably however I'd like to use something even shorter like this:
Events.handler(Handshake::class, { println(it.sent) })
或使用广告功能使用如下方法:
Events.handler(Handshake :: class){println(it.sent)}
Or use the advertised feature to use the method like this:
Events.handler(Handshake::class) { println(it.sent) }
这是我的活动
对象:
import java.util.*
import kotlin.reflect.KClass
object Events {
private val map = HashMap<Class<*>, Set<EventHandler<*>>>()
fun <T : Any> handler(eventType: KClass<T>, handler: EventHandler<T>) {
handler(eventType.java, handler)
}
fun <T> handler(eventType: Class<T>, handler: EventHandler<T>) = handlers(eventType).add(handler)
fun post(event: Any) = handlers(event.javaClass).forEach { it.handle(event) }
operator fun plus(event: Any) = post(event)
private fun <T> handlers(eventType: Class<T>): HashSet<EventHandler<T>> {
var set = map[eventType]
if (set == null) {
set = HashSet<EventHandler<*>>()
map.put(eventType, set)
}
return set as HashSet<EventHandler<T>>
}
}
我的 EventHandler
interface:
And my EventHandler
interface:
@FunctionalInterface
interface EventHandler<T> {
fun handle(event: T)
}
推荐答案
假设下面你真的需要 EventHandler
作为一个单独的接口(例如对于Java互操作)。如果不这样做,您可以简单地使用类型别名(因为Kotlin 1.1):
Assuming below that you really need EventHandler
as a separate interface (e.g. for Java interop). If you don't, you can simply use a type alias (since Kotlin 1.1):
typealias EventHandler<T> = (T) -> Unit
在这种情况下,简单的lambda将立即生效。
In this case a simple lambda will work right away.
但是如果你不想使用类型别名,问题仍然存在。 Kotlin只对Java中定义的函数进行SAM转换。由于 Events.handler
是在Kotlin中定义的,因此SAM转换不适用于它。
But if you don't want to use a type alias, the issue still stands. It is that Kotlin only does SAM-conversion for functions defined in Java. Since Events.handler
is defined in Kotlin, SAM-conversions do not apply to it.
支持此语法:
Events.handler(Handshake::class, EventHandler<Handshake> { println(it.sent) })
您可以定义一个名为 EventHandler
的函数:
You can define a function named EventHandler
:
fun <T> EventHandler(handler: (T) -> Unit): EventHandler<T>
= object : EventHandler<T> {
override fun handle(event: T) = handler(event)
}
支持这种语法:
Events.handler(Handshake::class, { println(it.sent) })
或者这个:
Events.handler(Handshake::class) { println(it.sent) }
你需要重载处理程序
函数来取代函数而不是 EventHandler
:
You need to overload the handler
function to take a function instead of EventHandler
:
fun <T> Events.handler(eventType: Class<T>, handler: (T) -> Unit) = EventHandler(handler)
注意:当未来版本的Kotlin具有类型别名时,将不需要 EventHandler
接口,因为它将被命名的别名替换为输入(T) - >单位
NOTE: When a future version of Kotlin has type aliases, the EventHandler
interface won't be needed, because it will be replaced by a named alias to the type (T) -> Unit
这篇关于Kotlin:使用lambda代替功能界面?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!