A `struct` groups related fields into one type; an `enum` gives names to a small set of states and is stored as an integer.
enum Status { None, Active, Closed }
struct Stake {
uint256 amount;
uint64 since;
Status status;
}
mapping(address => Stake) public stakes;Order struct fields so small types sit together — the compiler packs them into shared 32-byte slots and saves gas.