How do you implement a thread-safe lazy initialization in Rust?

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Accepted Answer

**LazyLock** (nightly) or **OnceLock** for thread-safe lazy init. **Using OnceLock:** ```rust use std::sync::OnceLock; static CONFIG: OnceLock = OnceLock::new(); fn get_config() -> &'static Config { CONFIG.get_or_init(|| Config { db_url: std::env::var("DATABASE_URL").unwrap(), max_connections: 10, }) } ``` **Using once_cell crate (stable):** ```rust use once_cell::sync::Lazy; static CONFIG: Lazy = Lazy::new(|| { Config { db_url: std::env::var("DATABASE_URL").unwrap(), } }); ``` **Key:** OnceLock for std, once_cell for stable lazy init.

Rust: How do you implement a thread-safe lazy initialization in Rust?