为什么java中不允许赋值给'this'？ [英] Why is assignment to 'this' not allowed in java?

问题描述

我从编译器得到的错误是赋值的左侧必须是变量。我的用例是深度复制，但并不是真正相关。

The error I get from the compiler is "The left hand side of an assignment must be a variable". My use case is deep copying, but is not really relevant.

在C ++中，可以分配给 * this 。

In C++, one can assign to *this.

问题不在于如何绕过这个的转让。这很简单，但是决定不让这个变量的背后有什么理由。

The question is not how to circumvent assignment to this. It's very simple, but rather what rationale is there behind the decision not to make this a variable.

是技术或概念的原因？

Are the reasons technical or conceptual?

我的猜测到目前为止 - 在随机方法中重建Object的可能性容易出错（概念性），但技术上可行。

My guess so far - the possibility of rebuilding an Object in a random method is error-prone (conceptual), but technically possible.

编辑请限制因为java规格如此说明的变体。我想知道决定的原因

EDIT Please restrain from variations of "because java specs say so". I would like to know the reason for the decision

推荐答案

在C ++中，可以分配给 * this

是的，但你不能在C ++中做 this = something ，我实际上认为这与你所询问的内容更接近在Java方面这里。

Yes, but you can't do this = something in C++, which I actually believe is a closer match for what you're asking about on the Java side here.

[...]决定不做的理由是什么这个一个变量。

我想说清晰度/可读性。

I would say clarity / readability.

这个被选为保留字，可能因为它没有作为显式参数传递一种方法。使用它作为普通参数并能够为其重新赋值，会严重损害可读性。

this was chosen to be a reserved word, probably since it's not passed as an explicit argument to a method. Using it as an ordinary parameter and being able to reassign a new value to it, would mess up readability severely.

事实上，很多人认为你不应该改变因此，参数变量完全存在。

In fact, many people argue that you shouldn't change argument-variables at all, for this very reason.

原因是技术性的还是概念性的？

Are the reasons technical or conceptual?

我认为主要是概念性的。但是会出现一些技术怪癖。如果你可以将值重新分配给这个，你可以完全隐藏局部变量后面的实例变量。

Mostly conceptual I would presume. A few technical quirks would arise though. If you could reassign a value to this, you could completely hide instance variables behind local variables for example.

我的猜测到目前为止 - 以随机方法重建对象的可能性容易出错（概念性），但技术上可行。

My guess so far - the possibility of rebuilding an Object in a random method is error-prone (conceptual), but technically possible.

我不确定我是否完全理解这个陈述，但是，容易出错可能是决定将其作为关键字的主要原因不是变量。

I'm not sure I understand this statement fully, but yes, error prone is probably the primary reason behind the decision to make it a keyword and not a variable.

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