OnceCell
OnceCell is a Rust cell type that permits a value to be initialized at most once and accessed thereafter.
Learn Rust in a Month of Lunches
OnceCell is a type that permits a value to be initialized once and subsequently accessed without repeated initialization.
- How it is used
- Deploys one-time initialization for values whose contents become available later, including global Logger configuration.
- How deep it goes
- Explains construction, set(), get(), synchronization choices, and a complete Logger example without descending into implementation internals.
- Examples
- Uses a global Logger whose URL is fetched later, then stores log entries protected by Mutex.
- What you can do after
- Apply it via OnceCell or OnceLock to initialize and later access a global Logger value.
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Idiomatic Rust
OnceCell is a Rust standard-library cell that permits a value to be initialized at most once and then accessed thereafter.
- How it is used
- Defers initialization when a value cannot be created in a single global-scope expression.
- How deep it goes
- Explains deferred initialization, interior mutability, and tradeoffs, but does not detail implementation internals.
- Examples
- Uses get_or_init to populate a vector of popular baby names.
- What you can do after
- Apply OnceCell through get_or_init to initialize a value within a function.
Related concepts
- thread localequivalent to · Thread-local data is data whose value or instance is independently associated with each executing thread.
- cellalternative to · Cell is a Rust standard-library type that provides interior mutability by allowing values to be retrieved or replaced through shared access without exposing references to its contents.
- standard librarypart of · A standard library is a collection of reusable modules, types, functions, APIs, and other facilities distributed with a programming language implementation or platform.
- lazy_staticalternative to · lazy_static is a Rust crate providing a macro for declaring static values initialized on first runtime access when compile-time initialization is insufficient.
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