interface-design

Interface Design

Interface Principles

Interfaces define the external API of your protocol. They are the contract between your system and its integrators.

// Minimal, focused interface — one concern per interface
interface IVault {
    function deposit(address token, uint256 amount) external returns (uint256 shares);
    function withdraw(address token, uint256 shares) external returns (uint256 amount);
    function balanceOf(address user, address token) external view returns (uint256);
}

// Separate admin interface
interface IVaultAdmin {
    function setFee(uint256 feeBps) external;
    function pause() external;
    function unpause() external;
}

// Separate events interface — inheritable without implementation obligation
interface IVaultEvents {
    event Deposited(address indexed user, address indexed token, uint256 amount, uint256 shares);
    event Withdrawn(address indexed user, address indexed token, uint256 amount, uint256 shares);
}

Abstract Contracts vs Interfaces

// Abstract contract: provides base implementation with extension points
abstract contract BaseVault is IVault, IVaultEvents, ReentrancyGuard {
    mapping(address => mapping(address => uint256)) internal _shares;

    function deposit(address token, uint256 amount)
        external
        virtual
        nonReentrant
        returns (uint256 shares)
    {
        shares = _convertToShares(token, amount);
        _shares[msg.sender][token] += shares;
        IERC20(token).safeTransferFrom(msg.sender, address(this), amount);
        emit Deposited(msg.sender, token, amount, shares);
    }

    // Extension point — subclasses define share calculation
    function _convertToShares(address token, uint256 amount)
        internal
        view
        virtual
        returns (uint256);
}