Roles library

The Roles library is used to store and manage different kinds of role-based access for contracts. As per your contract architecture needs, you can assign different kinds of roles to the different contracts or individual EOA accounts.

All of the role-related files are in the Chapter09/openzeppelin-solidity/contracts/access folder of the OpenZeppelin library.

Let's start by learning about a basic roles contract called Roles.sol. 

Managing roles using Roles.sol

Roles.sol is a generic library that stores the access rights that are provided to an address. All the roles-based contracts defined in OpenZeppelin use this library. It also exposes some internal functions that can only be called...