动态铸造在科特林 [英] Dynamic cast in Kotlin

问题描述

我想使用KClass<Int>将Any转换为Int，同时具有KClass<Int>和Any实际上是Int.

I want to cast Any to Int by using KClass<Int>, having a KClass<Int> and a Any which is actually Int.

fun <T> cast(any: Any, clazz: KClass<*>): T = clazz.java.cast(any) 

cast(0, Int::class)

但是，我遇到了这个错误.

However, I got this error.

java.lang.ClassCastException:无法将java.lang.Integer转换为int

java.lang.ClassCastException: Cannot cast java.lang.Integer to int

除了any as Int以外，您知道其他解决方案吗?

Do you know any solution except any as Int?

推荐答案

尝试将您的代码更改为

fun <T: Any> cast(any: Any, clazz: KClass<out T>): T = clazz.javaObjectType.cast(any) 

说明

由于参数any的类型为Any，因此它始终是引用类型，并且将对原语进行装箱.对于第二个参数，看来Kotlin反射将首选原始类型而不是引用类型，这就是为什么Int::class.java默认为ìnt而不是Integer的原因.通过使用javaObjectType，我们强制使用带框引用类型.

Explanation

Because the type of the parameter any is Any, it's always a reference type and primitives will be boxed. For the second parameter, it seems that Kotlin reflection will prefer primitive types to reference types, which is why Int::class.java will default to ìnt, not Integer. By using javaObjectType we force the usage of the boxed reference type.

您还可以使用以下函数定义:

You could also use the following function definition:

inline fun <reified T: Any> cast(any: Any): T = T::class.javaObjectType.cast(any) 

// usage

cast<Int>(0)

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