Design Patterns & Upgrades

Common smart contract patterns include: Access Control (role-based permissions), Pull vs Push payments (users withdraw rather than contract sends), Factory pattern (contract creates other contracts), Proxy pattern (upgradeable contracts via delegatecall). The most popular upgrade pattern is UUPS (Universal Upgradeable Proxy Standard). Important: upgradeable contracts must be initialized (not constructed), storage layout must be preserved across upgrades, and a governance mechanism should control who can upgrade.