RefCell<T> and the Interior Mutability Pattern

# Introduction

Welcome to **RefCell<T> and the Interior Mutability Pattern**. This lab is a part of the [Rust Book](https://doc.rust-lang.org/book/). You can practice your Rust skills in LabEx.

In this lab, we will explore the concept of interior mutability in Rust and how it is implemented using the `RefCell<T>` type.