在R中声明Const变量 [英] Declaring a Const Variable in R

问题描述

我正在R中工作，我想定义一些我（或我的合作者之一）无法更改的变量。在C ++中，我可以这样做：

I'm working in R, and I'd like to define some variables that I (or one of my collaborators) cannot change. In C++ I'd do this:

const std::string path( "/projects/current" );

如何用R编程语言做到这一点？

How do I do this in the R programming language?

为清楚起见进行编辑：我知道我可以在R中定义这样的字符串：

Edit for clarity: I know that I can define strings like this in R:

path = "/projects/current"

我真正想要的是一种语言结构，可以保证没有人可以更改相关的值

What I really want is a language construct that guarantees that nobody can ever change the value associated with the variable named "path."

编辑以响应评论：

从技术上讲，const是一个编译时保证，但是在我看来R解释器将抛出一条错误消息来停止执行，这在我看来是有效的。例如，看看当您尝试将值分配给数字常量时发生了什么。

It's technically true that const is a compile-time guarantee, but it would be valid in my mind that the R interpreter would throw stop execution with an error message. For example, look what happens when you try to assign values to a numeric constant:

> 7 = 3
Error in 7 = 3 : invalid (do_set) left-hand side to assignment

所以我真正想要的是一种语言功能，该功能允许您一次只分配一次值，并且在尝试为声明为const的变量分配新值时应该出现某种错误。我不在乎该错误是否在运行时发生，尤其是在没有编译阶段的情况下。从维基百科的定义上看，从技术上讲，这可能不是const，但是非常接近。在R编程语言中，这似乎也不可能。

So what I really want is a language feature that allows you to assign values once and only once, and there should be some kind of error when you try to assign a new value to a variabled declared as const. I don't care if the error occurs at run-time, especially if there's no compilation phase. This might not technically be const by the Wikipedia definition, but it's very close. It also looks like this is not possible in the R programming language.

推荐答案

请参见 lockBinding ：

a <- 1
lockBinding("a", globalenv())
a <- 2
Error: cannot change value of locked binding for 'a'

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