Lazy Structs

Lazy initialization types

LazyCell (Rust 1.80+)

use std::cell::LazyCell;

fn main() {
    // LazyCell - single-threaded lazy init
    let lazy: LazyCell<String> = LazyCell::new(|| {
        println!("Initializing...");
        String::from("Hello, Lazy!")
    });

    println!("Before access");
    println!("Value: {}", *lazy);  // Initializes here
    println!("Again: {}", *lazy);  // Already initialized

    // Not initialized if never accessed
    let never_used: LazyCell<String> = LazyCell::new(|| {
        println!("This won't print");
        String::new()
    });
    println!("\nnever_used created but not accessed");
    drop(never_used);

    // In struct
    struct Config {
        data: LazyCell<String>,
    }

    let config = Config {
        data: LazyCell::new(|| {
            println!("Loading config...");
            "config value".to_string()
        }),
    };

    println!("\nConfig data: {}", *config.data);
}