从Java类调用Kotlin数据类复制功能不起作用 [英] Kotlin data class copy function not working when called from java class

问题描述

也许我误解了data类的copy函数的工作方式，或者可能是一个错误，但是以下是copy函数无法正常工作的示例:

Maybe I'm misinterpreting how the copy function of a data class works or maybe there's a bug, but the following is an example of the copy function not working as expected:

科特琳:

data class A {
    public var x: String? = null
    public var y: String? = null
    public var z: B = B.ONE
}

enum class B {
    ONE
    TWO
    THREE
}

Java

A a1 = new A()
a1.setX("Hello")
a1.setY("World")
a1.setZ(B.TWO)

A a2 = a1.copy()
// a2.x is null
// a2.y is null
// a2.z is B.ONE

似乎copy只是在创建A的新实例，而不是复制值.如果我将变量放入构造函数中，则将分配值，但这与构造新实例没有什么不同.

It seems that copy is just making a new instance of A and not copying the values. If I put the variables in the constructor, the values are assigned, but then it's no different than constructing a new instance.

推荐答案

好的，我在文档中错过了这句话:

Okay, I missed this sentence in the docs:

如果这些函数中的任何一个在类主体中显式定义或从基本类型继承，则不会生成.

If any of these functions is explicitly defined in the class body or inherited from the base types, it will not be generated.

实际上，这使得copy并不比Java互操作的构造函数好.

Which, infact, makes copy no better than a constructor for Java interop.

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