Data structures and storage

Store data efficiently on-chain.

📖 Key ideas

Mappings: mapping(address => uint256) balances;
Arrays and structs group data.
Data locations: storage (persistent), memory (temporary), calldata (read-only input).
Storage writes are expensive in gas.
Avoid unbounded loops over large arrays.

💡 Real-life example: Storage is writing in a permanent register; memory is scribbling on scratch paper.

mappingKey-value store

structCustom grouped type

storagePersistent contract data

calldataRead-only function input