Solidity Dev

function withdraw(uint256 amount) external {
    // CHECKS
    require(balances[msg.sender] >= amount, "Insufficient balance");

    // EFFECTS
    balances[msg.sender] -= amount;

    // INTERACTIONS
    (bool success, ) = msg.sender.call{value: amount}("");
    require(success, "Transfer failed");
}

Custom Errors (Gas Efficient)

// Instead of require strings
error InsufficientBalance(uint256 requested, uint256 available);
error Unauthorized(address caller);

function withdraw(uint256 amount) external {
    if (balances[msg.sender] < amount) {
        revert InsufficientBalance(amount, balances[msg.sender]);
    }
}

Unchecked Arithmetic

function increment(uint256 i) external pure returns (uint256) {
    // Safe when overflow is impossible
    unchecked {
        return i + 1; // Saves ~80 gas
    }
}

ERC Standard Templates

ERC-20 Token

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Permit.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Votes.sol";

contract GovernanceToken is ERC20, ERC20Permit, ERC20Votes {
    constructor() ERC20("MyToken", "MTK") ERC20Permit("MyToken") {
        _mint(msg.sender, 1000000 * 10**decimals());
    }

    // Required overrides for multiple inheritance
    function _afterTokenTransfer(address from, address to, uint256 amount)
        internal override(ERC20, ERC20Votes)
    {
        super._afterTokenTransfer(from, to, amount);
    }

    function _mint(address to, uint256 amount)
        internal override(ERC20, ERC20Votes)
    {
        super._mint(to, amount);
    }

    function _burn(address account, uint256 amount)
        internal override(ERC20, ERC20Votes)
    {
        super._burn(account, amount);
    }
}

ERC-721 NFT

import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721Royalty.sol";

contract MyNFT is ERC721, ERC721URIStorage, ERC721Royalty {
    uint256 private _tokenIdCounter;

    constructor() ERC721("MyNFT", "NFT") {
        _setDefaultRoyalty(msg.sender, 250); // 2.5%
    }

    function safeMint(address to, string memory uri) external {
        uint256 tokenId = _tokenIdCounter++;
        _safeMint(to, tokenId);
        _setTokenURI(tokenId, uri);
    }
}

Upgradeable Contract Pattern

UUPS Proxy

import "@openzeppelin/contracts-upgradeable/proxy/utils/UUPSUpgradeable.sol";
import "@openzeppelin/contracts-upgradeable/access/OwnableUpgradeable.sol";

contract MyContractV1 is UUPSUpgradeable, OwnableUpgradeable {
    uint256 public value;

    /// @custom:oz-upgrades-unsafe-allow constructor
    constructor() {
        _disableInitializers();
    }

    function initialize() public initializer {
        __Ownable_init();
        __UUPSUpgradeable_init();
    }

    function _authorizeUpgrade(address newImplementation)
        internal override onlyOwner
    {}

    function setValue(uint256 _value) external {
        value = _value;
    }
}

Gas Optimization Techniques

Storage Packing

// BAD: Uses 3 storage slots (96 bytes)
contract Unpacked {
    uint256 a;    // slot 0
    uint8 b;      // slot 1
    uint256 c;    // slot 2
}

// GOOD: Uses 2 storage slots (64 bytes)
contract Packed {
    uint256 a;    // slot 0
    uint256 c;    // slot 1
    uint8 b;      // slot 1 (packed with previous)
}

Calldata vs Memory

// Use calldata for read-only arrays
function processData(uint256[] calldata data) external pure returns (uint256) {
    uint256 sum;
    for (uint256 i; i < data.length;) {
        sum += data[i];
        unchecked { ++i; }
    }
    return sum;
}

Assembly Optimization

function efficientTransfer(address to, uint256 amount) external {
    assembly {
        // Load balance from storage
        let bal := sload(add(balances.slot, caller()))

        // Check balance
        if lt(bal, amount) {
            revert(0, 0)
        }

        // Update balances
        sstore(add(balances.slot, caller()), sub(bal, amount))
        sstore(add(balances.slot, to), add(sload(add(balances.slot, to)), amount))
    }
}

Process Integration

This skill integrates with:

Tools Reference

Best Practices Checklist

• Use latest stable Solidity version (0.8.x+)
• Implement CEI pattern for external calls
• Use custom errors instead of require strings
• Add NatSpec documentation
• Implement proper access control
• Consider gas optimization
• Add comprehensive tests
• Run static analysis (Slither)
• Document upgrade paths

See Also

• skills/foundry-framework/SKILL.md - Foundry development
• skills/hardhat-framework/SKILL.md - Hardhat development
• skills/openzeppelin/SKILL.md - OpenZeppelin contracts
• skills/gas-optimization/SKILL.md - Gas optimization
• agents/solidity-auditor/AGENT.md - Security auditor agent