Standard vs. Upgradeable - Whats the difference?

OpenZeppelin provides two distinct types of contracts: standard contracts and upgradeable contracts. Understanding the difference between these two is from utmost importance.

The OpenZeppelin contracts repository contains standard smart contracts designed to be inherited by your own contracts. These contracts cover a wide range of common use cases, including token creation (ERC20, ERC721), security features (ReentrancyGuard, Ownable), and access control mechanisms (Roles, AccessControl). The idea is to provide developers with a solid foundation, allowing them to focus on building the unique aspects of their project rather than reinventing the wheel.

On the other hand, OpenZeppelin upgradeable contracts are specifically designed for use with proxy contracts. These contracts cover to the need for upgradability in smart contracts. Upgradability is crucial for fixing bugs and enhancing contract functionality over time without losing the state or having to deploy a new contract. The upgradeable contracts follow a different architectural pattern, necessitating a distinct approach to initialization and state management.
Why the Distinction?

At first glance, it might seem weird to have two separate repositories for standard and upgradeable contracts. However, this separation addresses specific technical necessities associated with upgradeable smart contracts:

Initializers over Constructors

Upgradeable Contracts Need Initializers: Unlike traditional smart contracts that use constructors to initialize contract state, upgradeable contracts must use initializer functions. This is because the proxy pattern used for upgradeability does not support the direct use of constructors. Initializers ensure that state variables are set correctly when the contract is first used, rather than when it's deployed.

Storage Collision Prevention

Storage Layout and the gap[] Variable: Upgradeable contracts must be carefully designed to prevent storage collisions between different contract versions. This is where the gap[] variable comes into play. By including a reserved space in the contract's storage layout, developers can add new variables in future versions without risking collisions with existing ones. This technique ensures that the contract's state remains consistent and predictable across upgrades.

Understanding the difference between OpenZeppelin's standard and upgradeable contracts is essential for Solidity developers. While both are designed to be inherited and provide a secure, community-vetted foundation for smart contract development, they cater to distinct needs—standard contracts for a solid, unchanging foundation, and upgradeable contracts for flexibility and evolution over time.