【Rust Cookbook系列】十四 内存管理

1. 常量

  需要安装lazy_static库，可通过cargo add lazy_static 命令安装

[dependencies]
lazy_static = "1.4.0"

1.1 声明延迟计算常量

  声明延迟计算的常量 HashMap。HashMap 将被计算一次，随后存储在全局静态（全局堆栈）引用。

use lazy_static::lazy_static;
use std::collections::HashMap;

lazy_static! {
    static ref PRIVILEGES: HashMap<&'static str, Vec<&'static str>> = {
        let mut map = HashMap::new();
        map.insert("James", vec!["user", "admin"]);
        map.insert("Jim", vec!["user"]);
        map
    };
}

fn show_access(name: &str) {
    let access = PRIVILEGES.get(name);
    println!("{}: {:?}", name, access);
}

fn main() {
    let access = PRIVILEGES.get("James");
    println!("James: {:?}", access);

    show_access("Jim");
}

• 运行cargo run输出

James: Some(["user", "admin"])
Jim: Some(["user"])