RefCellT

RefCellT is a generic Rust struct that provides interior mutability. It allows mutable borrows of data even when the reference to the RefCellT is immutable. This is achieved through runtime borrow checking, which ensures that at any given point in time, there is either only one mutable borrow or any number of immutable borrows, but not both.

The primary purpose of RefCellT is to enable patterns where data needs to be modified within an immutable context, which is common in scenarios like implementing certain data structures or working with callback functions where ownership might be complex. It is part of Rust's standard library, specifically within the std::cell module.

When using RefCellT, you typically call its `borrow()` method to obtain an immutable reference to the contained data, or `borrow_mut()` to get a mutable reference. These methods will panic at runtime if the borrowing rules are violated. This makes RefCellT a tool for situations where compile-time checks are insufficient or overly restrictive, but it comes with the trade-off of runtime overhead and potential panics if not used carefully.

RefCellT is not thread-safe. For thread-safe interior mutability, Rust provides `Mutex` and `RwLock` from the `std::sync` module. RefCellT is intended for single-threaded scenarios where its performance benefits over thread-safe alternatives are desirable. Its use is often a sign that a program's ownership and borrowing design might benefit from rethinking, but it serves as a necessary escape hatch in specific programming paradigms.