Question 1

How does Solidity pack struct members into storage slots?

Accepted Answer

Solidity packs struct members sequentially in declaration order. Each member starts where the previous one ended within the current 32-byte slot. If the next member doesn't fit in the remaining space, a new slot is started. Members are never split across slots. Packing is right-to-left within each slot.

Question 2

What is the best ordering strategy for struct members?

Accepted Answer

Sorting members by size (smallest first) generally produces the tightest packing. Small types like bool (1 byte), uint8 (1 byte), and uint16 (2 bytes) can share a slot, while large types like uint256 (32 bytes) always need their own slot regardless of position. Grouping small types together minimizes wasted space.

Question 3

How much gas can struct packing optimization save?

Accepted Answer

Each storage slot saved eliminates 20,000 gas from contract deployment and 5,000 gas from subsequent writes. A struct with 5 wasted slots costs 100,000 extra gas on deployment alone. For frequently-called functions, these savings multiply with every transaction.

Member	Type	Slot	Offset	Size
owner	address	0	0	20B
totalSupply	uint256	1	0	32B
decimals	uint8	2	0	1B
paused	bool	2	1	1B

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