1，关键字by修饰类，表示类委托
interface Animation{fun eat()
}//动态代理
class Dog:Animation{override fun eat() {println("dog eat oligarch")}
}class DogProxy:Animation by Dog(){}

2,关键字by修饰变量，实现属性委托

var name:String by NameDelegate()class NameDelegate:ReadWriteProperty<Any?,String>{override fun getValue(thisRef: Any?, property: KProperty<*>): String {println(property.name)return property.name}override fun setValue(thisRef: Any?, property: KProperty<*>, value: String) {println(value)}
}

3，operator修饰方法，表示重写操作符

lateinit var mList:MyList<Int>
mList.plus(1)
mList+1
interface MyList<out T>{fun get(index:Int):Toperator fun plus(t: @UnsafeVariance T)operator fun div(t: @UnsafeVariance T)operator fun minus(t: @UnsafeVariance T)
}

kotlin所有运算操作符:

一元操作符（Unary Operators）
+a	a.unaryPlus()
-a	a.unaryMinus()
!a	a.not()
a++	a.inc()
二元操作符（  Binary Operators）