为什么C＃不提供const类似于C ++？ [英] Why doesn't C# offer constness akin to C++?

问题描述

C＃中的引用与C ++中的引用非常相似，只是它们是垃圾回收的。

为什么C＃编译器很难支持以下操作：

1. 成员函数标记为 const 。


2. 引用数据类型（字符串除外） const ，可以调用 const 成员函数？



我相信如果C＃支持这将是非常有用的。一个，它真的会帮助看起来广泛的同性恋放弃哪些C＃程序员返回对私人数据的裸露引用（至少这是我在我的工作场所看到的）。

还是已经有一些等价的C＃，我错过了？ （我知道 readonly 和 const 关键字，但它们不能真正满足上述目的）

解决方案

我怀疑有一些实际原因，有一些理论原因：

• 常数应用于对象或参考吗？如果它在引用，这应该是编译时只，还是在参考本身的一点？


• 你能不能像在C ++中那样把它丢弃？这听起来不像你想在托管平台上的东西...但是在C ++中所有那些有意义的时候呢？


• 语法变得棘手（IMO）当你有一个以上的类型涉及到一个声明 - 想到数组，泛型等。它可能变得很难确定哪个位是const。


• 如果你不能抛弃它，每个人都必须正确。换句话说，.NET框架类型和任何其他第三方库使用都必须做正确的事情，或者你留下的错误的情况下，你的代码不能做正确的事情，因为一个微妙的问题， const。

有一个很大的原因，为什么现在不能支持 / p>

• 向后兼容性：没有办法将所有库正确迁移到它，使得它几乎无用：（

我同意有一些常数指示器，但我看不到它发生，恐怕。

编辑：有一个关于Java社区中这种肆虐的争论，有关相关错误您可能会感兴趣。

References in C# are quite similar to those on C++, except that they are garbage collected.

Why is it then so difficult for the C# compiler to support the following:

1. Members functions marked const.
2. References to data types (other than string) marked const, through which only const member functions can be called ?

I believe it would be really useful if C# supported this. For one, it'll really help the seemingly widespread gay abandon with which C# programmers return naked references to private data (at least that's what I've seen at my workplace).

Or is there already something equivalent in C# which I'm missing? (I know about the readonly and const keywords, but they don't really serve the above purpose)

解决方案

I suspect there are some practical reasons, and some theoretical reasons:

• Should the constness apply to the object or the reference? If it's in the reference, should this be compile-time only, or as a bit within the reference itself? Can something else which has a non-const reference to the same object fiddle with it under the hood?
• Would you want to be able to cast it away as you can in C++? That doesn't sound very much like something you'd want on a managed platform... but what about all those times where it makes sense in C++?
• Syntax gets tricky (IMO) when you have more than one type involved in a declaration - think arrays, generics etc. It can become hard to work out exactly which bit is const.
• If you can't cast it away, everyone has to get it right. In other words, both the .NET framework types and any other 3rd party libraries you use all have to do the right thing, or you're left with nasty situations where your code can't do the right thing because of a subtle problem with constness.

There's a big one in terms of why it can't be supported now though:

• Backwards compatibility: there's no way all libraries would be correctly migrated to it, making it pretty much useless :(

I agree it would be useful to have some sort of constness indicator, but I can't see it happening, I'm afraid.

EDIT: There's been an argument about this raging in the Java community for ages. There's rather a lot of commentary on the relevant bug which you may find interesting.

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