Storage, reentrancy, gas, and the structural decisions that separate contracts that survive from contracts that drain.
I have written my share of Solidity. The contract that taught me the most was not a DeFi product — it was a small NFT minting contract for a client, and it worked perfectly on testnet. On mainnet it cost users roughly $180 more per mint than our estimate said it should. The logic was right. The storage layout was wrong, and every single transaction paid for it.
That experience pushed me to systematize everything I now apply on every contract I ship. This is not a Solidity tutorial from scratch — I assume you know the language basics. This is the pattern guide I wish someone had handed me before that mint: how to lay out storage, why order of operations can drain your treasury, how to spend less gas per call, and the failure modes that show up only after you deploy.
Before Anything: Know What Gas Actually Buys
Every pattern below exists for one of two reasons: correctness under adversarial conditions, or raw cost per operation. You need both in your head before you write a single line.
