ERC-4626 — tokenized vaults

Before 4626, every vault had a custom deposit/withdraw API. If you wanted to aggregate yield across Yearn + Aave + Compound, you wrote three integrations. 4626 standardized the interface.

solidity
// Deposit underlying, get shares
function deposit(uint256 assets, address receiver) external returns (uint256 shares);
function mint(uint256 shares, address receiver) external returns (uint256 assets);

// Redeem shares, get underlying
function withdraw(uint256 assets, address receiver, address owner) external returns (uint256 shares);
function redeem(uint256 shares, address receiver, address owner) external returns (uint256 assets);

// Previews (view — what WOULD a deposit/withdraw yield right now)
function previewDeposit(uint256 assets) external view returns (uint256 shares);
function previewWithdraw(uint256 assets) external view returns (uint256 shares);
function previewMint(uint256 shares) external view returns (uint256 assets);
function previewRedeem(uint256 shares) external view returns (uint256 assets);

// Totals
function totalAssets() external view returns (uint256);
function convertToShares(uint256 assets) external view returns (uint256);
function convertToAssets(uint256 shares) external view returns (uint256);

solidity
import "@openzeppelin/contracts/token/ERC20/extensions/ERC4626.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

contract YieldVault is ERC4626 {
    constructor(IERC20 asset_) ERC20("YieldVault", "yUSDC") ERC4626(asset_) {}
    // Done. You've got a share-based vault.
}

Inheriting ERC4626 gives you all the deposit/withdraw/preview logic. To add yield, you override totalAssets() to account for earnings (from an external protocol, swaps, whatever strategy).

On first deposit to an empty vault, an attacker can: 1. Deposit 1 wei → gets 1 share 2. Transfer 1e18 wei directly to the vault (not via deposit) 3. totalAssets = 1 + 1e18, shares = 1 4. Next depositor who deposits 1e18 gets 0 shares (rounded down)

OZ's 4626 mitigates this with a small "virtual share" offset. Always set decimalsOffset() to 6+ when you inherit.

Write a YieldVault that:

• Inherits ERC4626
• Takes an underlying IERC20 in the constructor
• Names the share token "YieldVault" / "yUSDC"