包中的全局变量 - 更推荐哪种方法?

问题描述

我知道全局变量通常是邪恶的，我应该避免它们，但如果我的包确实需要一个全局变量，这两种方法中哪一种更好?还有其他推荐的方法吗?

I do understand that generally global variables are evil and I should avoid them, but if my package does need to have a global variable, which of these two approaches are better? And are there any other recommended approaches?

1. 使用对包可见的环境

1. Using an environment visible to the package

pkgEnv <- new.env()
pkgEnv$sessionId <- "xyz123"

使用选项

options("pkgEnv.sessionId" = "xyz123")

我知道还有一些其他线程询问如何实现全局变量，但我没有看到关于推荐哪个的讨论

I know there are some other threads that ask about how to achieve global variables, but I haven't seen a discussion on which one is recommended

推荐答案

一些包使用隐藏变量(以 . 开头的变量)，例如 .Random.seed和 .Last.value 在基础 R 中做.在你的包中你可以做

Some packages use hidden variables (variables that begin with a .), like .Random.seed and .Last.value do in base R. In your package you could do

e <- new.env()
assign(".sessionId", "xyz123", envir = e)
ls(e)
# character(0)
ls(e, all = TRUE)
# [1] ".sessionId"

但是在你的包中你不需要指定e.您可以使用 .onLoad() 挂钩在加载包时分配变量.

But in your package you don't need to assign e. You can use a .onLoad() hook to assign the variable upon loading the package.

.onLoad <- function(libname, pkgname) {
    assign(".sessionId", "xyz123", envir = parent.env(environment()))
}

请参阅 this question 及其答案，了解有关包变量的一些很好的解释.

See this question and its answers for some good explanation on package variables.

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