//! This crate provides a type whose value remains unchanged even when accessed through a mutable reference.
//! Some functions are compatible with `no_std` environments.
//!
//! | Module | Characteristics | Feature Flags |
//! |---------------|-------------------------------------------|-----------------------------|
//! | `unsync` | `!Sync`, `!Send` type<br>Supports `no_std`| `default`, `all`, `no_std`, `unsync` |
//! | `mutex` | `Sync`, `Send` type using `std::sync::Mutex` | `default`, `all`, `mutex` |
//! | `rwlock` | `Sync`, `Send` type using `std::sync::RwLock` | `default`, `all`, `rwlock` |