Testy Environ - 一种环境形式，可以设置可以静态访问的作用域有限值

.摘要 [来源，toml]

include::Cargo.toml[lines=2..5]

.描述

include::src/lib.rs[tag=description]

lib.rs:

安全的全局对堆变量的引用。

使用 environ! 宏设置全局引用，并为其指定名称和类型。使用其名称下作用域内的 using 函数来命名引用并调用一个不接受任何参数但可以通过 with 函数访问该引用的函数。

示例

#[macro_use] extern crate environ;
// create a place for the global reference to exist.
environ!(counter: u32);
fn stuff() {
  // do some stuff, accessing the named reference as desired.
  counter::with(|i| *i += 1);
}
fn main() {
  // declare a stack variable of the same type as our global declaration.
  let mut counter_value = 41u32;
  // call stuff, setting up our `counter` environment as a reference to our counter_value var.
  counter::using(&mut counter_value, stuff);
  println!("The answer is {:?}", counter_value); // will print 42!
  stuff();	// safe! doesn't do anything.
}