Solidity, re-entrancy, and EVM gas optimization.
3 questions in Blockchain & Web3.
A reentrancy attack happens when a smart contract calls an untrusted address before updating its own state, letting the callee enter again and reuse stale balances. The checks-effects-interactions pattern closes that window by validating first, mutating state next and calling out last.
Solidity storage layout dominates gas cost because persistent 32-byte slots are expensive to read and write on every node. Efficient smart contracts pack fields, cache repeated storage reads, avoid unnecessary writes and preserve layout during upgrades.
The proxy upgradeability pattern keeps state in the proxy and delegates calls to replaceable implementation logic, which makes storage layout, initializers and upgrade admin control the core smart contract security risks. Use this solidity answer to show the decision, trade-off, and evidence rather than a memorised definition.