fix: make LazyLock example demonstrate realistic applicatino

Author: JayanAXHF

src/mem/global_static/lazy-constant.md

@@ -79,25 +79,28 @@ The [`LazyLock`] type is a thread-safe alternative to [`LazyCell`].
 use std::sync::LazyLock;
 use std::collections::HashMap;
 
-static PRIVILEGES: LazyLock<HashMap<&'static str, Vec<&'static str>>> = LazyLock::new(|| {
-    {
-        let mut map = HashMap::new();
-        map.insert("James", vec!["user", "admin"]);
-        map.insert("Jim", vec!["user"]);
-        map
+struct Config {
+    api_key: String,
+    timeout: u64,
+}
+
+// Imagine loading this from a .env file or a vault
+static APP_CONFIG: LazyLock<Config> = LazyLock::new(|| {
+    println!("Loading configuration...");
+    Config {
+        api_key: std::env::var("API_KEY").unwrap_or_else(|_| "default_key".to_string()),
+        timeout: 30,
     }
 });
 
-fn show_access(name: &str) {
-    let access = PRIVILEGES.get(name);
-    println!("{}: {:?}", name, access);
-}
-
 fn main() {
-    let access = PRIVILEGES.get("James");
-    println!("James: {:?}", access);
+    println!("App started.");
 
-    show_access("Jim");
+    // The closure above isn't run until we access APP_CONFIG here.
+    let timeout = APP_CONFIG.timeout;
+    
+    println!("Timeout is: {}s", timeout);
+    println!("API Key is hidden: {}", APP_CONFIG.api_key.len() > 0);
 }
 ```
 [`LazyLock`]: https://doc.rust-lang.org/std/sync/struct.LazyLock.html