Gas Optimisation Basics — Hands-on lab

Measured steps Benchmark first. Apply one change at a time and keep the ones that meaningfully help. Add tests/invariants that encode any assumptions (like bounds for unchecked math).

The root problem with conventional currency is all the trust that’s required to make it work.

— Satoshi Nakamoto

Documentation Inline comment why an unchecked block is safe or why packing is used. Include before/after gas numbers in PR descriptions for future readers.

Guardrails Avoid unbounded loops over user-controlled arrays; consider batching. Keep CEI and reentrancy guards intact even if they cost a few gas.

function sum(uint256[] memory xs) internal pure returns (uint256 total) {
    uint256 len = xs.length;
    for (uint256 i; i < len; ) {
        total += xs[i];
        unchecked { ++i; } // safe because i<len is loop guard
    }
}

function transferMany(address[] calldata to, uint256 amount) external {
    uint256 len = to.length;
    for (uint256 i; i < len; ) {
        _transfer(msg.sender, to[i], amount);
        unchecked { ++i; }
    }
}