### OnceCell API Overview

Source: https://github.com/matklad/once_cell/blob/master/README.md

Illustrates the basic API for OnceCell, including initialization, setting a value, and retrieving it.

```rust
impl OnceCell<T> {
    fn new() -> OnceCell<T> { ... }
    fn set(&self, value: T) -> Result<(), T> { ... }
    fn get(&self) -> Option<&T> { ... }
}
```

--------------------------------

### Lazy Initialization with sync::Lazy

Source: https://github.com/matklad/once_cell/blob/master/README.md

Demonstrates using `sync::Lazy` to lazily initialize a static Mutex-protected HashMap, providing a macro-free alternative to lazy_static!.

```rust
use std::{sync::Mutex, collections::HashMap};
use once_cell::sync::Lazy;

static GLOBAL_DATA: Lazy<Mutex<HashMap<i32, String>>> = Lazy::new(|| {
    let mut m = HashMap::new();
    m.insert(13, "Spica".to_string());
    m.insert(74, "Hoyten".to_string());
    Mutex::new(m)
});

fn main() {
    println!("{:?}", GLOBAL_DATA.lock().unwrap());
}
```

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