使用动态代理为接口创建空实现

组件化时，组件需要暴露一些接口给外部。

而当组件的实现没有被装载时，我们希望调用者不用进行逻辑判断，执行代码时自动会执行一段空实现，当我们有海量接口时，自动创建空实现也许是一种省事的方法。

抄下面代码就完事了。

object NoOpImplement {

    private const val TAG = "NoOpImplement"

    private val classMap = mutableMapOf<Class<out Any>, Any>()

    fun <T : Any> get(clazz: Class<T>): T {
        val found = classMap[clazz]
        return (if (found == null) {
            val impl = Proxy.newProxyInstance(clazz.classLoader,
                arrayOf<Class<*>>(clazz), NoOpInvocationHandler)
            classMap[clazz] = impl
            impl
        } else {
            found
        }) as T
    }

    object NoOpInvocationHandler : InvocationHandler {
        override operator fun invoke(o: Any?, method: Method, objects: Array<Any?>?): Any? {
            val type: Type = method.returnType
            val result: Any? = when {
                Boolean::class.javaPrimitiveType == type -> {
                    false
                }
                Byte::class.javaPrimitiveType == type -> {
                    0.toByte()
                }
                Char::class.javaPrimitiveType == type -> {
                    0.toChar()
                }
                Short::class.javaPrimitiveType == type -> {
                    0.toShort()
                }
                Int::class.javaPrimitiveType == type -> {
                    0
                }
                Long::class.javaPrimitiveType == type -> {
                    0L
                }
                Float::class.javaPrimitiveType == type -> {
                    0.0f
                }
                Double::class.javaPrimitiveType == type -> {
                    0.0
                }
                else -> null
            }
            Log.v(TAG, "invoke no-op ${method.name} $result")
            return result
        }
    }
}