问题描述
我正在尝试在服务启动时从系统环境中加载密码和敏感数据.我尝试了多种不同的方法，但似乎无法找出在Rust中执行此操作的正确方法.
I'm trying to load passwords and sensitive data from the system's environment when my service starts up. I've tried a number of different ways but can't seem to figure out the right way to do this in Rust.
const PASSWORD: String = var("PASSWORD").unwrap();
不起作用，因为method calls in constants are limited to constant inherent methods. static也是如此(显然错误是静态的).
Doesn't work because method calls in constants are limited to constant inherent methods. The same applies to static (except the error says statics, obviously).
我看到的另一种方式是
const PASSWORD: &'static str = env!("PASSWORD");
但是问题在于它会在编译时定义，因为env!是一个宏(至少这是我的理解).
But the problem with that is it will be defined at compile time as env! is a macro (at least that is my understanding).
我还考虑过将对var("...").unwrap()的调用仅包装在一个函数中，但是该解决方案并不适合我，而且还允许在整个运行时更改值，并且在服务启动时不对其进行验证.
I also considered simply wrapping the call to var("...").unwrap() in a function but that solution doesn't really sit right with me, and would also allow the values to change throughout runtime AND not validate them when the service starts.
您可以说我是Rust的新手.如果您在回答中不能仅解释如何在运行时加载const/static，还可以解释为什么我在做的是愚蠢的和错误的，我将不胜感激:)
As you can tell I'm new to Rust. I'd really appreciate if in your answer you could not just explain how to load the const/static at runtime but also explain why what I'm doing is dumb and wrong :)
推荐答案
const和static在Rust中扮演不同的角色.
const and static fill different roles in Rust.
const不仅表示常量，还表示 compile-time 常量，该值是在编译时确定的，并写入程序的只读存储器中.它不适合您的用例.
const does not only mean a constant, it means a compile-time constant, a value determined at compile-time and inscribed in the read-only memory of the program. It is not suitable for your usecase.
static表示全局变量，其生存期将遍及整个程序.它可能是可变的，在这种情况下，必须为Sync以避免并行修改.必须从常量中初始化static变量，以便从程序开始就可以使用它.
static means a global variable, with a lifetime that will span the entire program. It may be mutable, in which case it must be Sync to avoid concurrent modifications. A static variable must be initialized from a constant, in order to be available from the start of the program.
那么，如何在运行时读取变量并使变量可用?好吧，一个干净的解决方案是完全避免全局变量.
So, how to read a variable at run-time and have it available? Well, a clean solution would be to avoid globals altogether...
...但由于它很方便，因此有一个包装箱: lazy_static! .
... but since it can be convenient, there is a crate for it: lazy_static!.
use std::env::var;
use lazy_static::lazy_static;
lazy_static! {
static ref PASSWORD: String = var("PASSWORD").unwrap();
}
fn main() {
println!("{:?}", *PASSWORD);
}
第一次访问该变量时，将执行该表达式以加载其值，然后将该值存储起来并可用，直到程序结束为止.
On first access to the variable, the expression is executed to load its value, the value is then memorized and available until the end of the program.
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