如何使用toString扩展数据类 [英] How to extend a data class with toString

问题描述

我创建了一个数据类

data class Something (
    val a : String,
    val b : Object,
    val c : String
)

稍后在我的程序中，我需要尝试扩展toString方法的该数据类的字符串表示形式.

as later in my program, I need the string representation of this data class I tried to extend the toString method.

override fun Something.toString() : String = a + b.result() + c

这里的问题是，它不允许扩展(覆盖)toString函数，因为它不适用于顶级函数.

The problem here is, it does not allow extending (overriding) the toString function, as it is not applicable to top-level functions.

如何正确覆盖/扩展自定义数据类的toString方法?

How to properly override/extend the toString method of a custom dataclass?

推荐答案

在Kotlin中，扩展功能无法覆盖成员函数，而且

In Kotlin, extension functions cannot override member functions, moreover, they are resolved statically. It implies that if you write an extension function fun Something.toString() = ..., s.toString() won't be resolved to it, because member always wins.

但是在您的情况下，没有什么能阻止您覆盖Something类主体内的toString，因为data类可以像常规类一样具有主体:

But in your case, nothing stops you from overriding toString inside Something class body, because data classes can have bodies just like regular classes:

data class Something(
    val a: String,
    val b: Any,
    val c: String
) {
    override fun toString(): String = a + b + c
}

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