Variable packing in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is variable packing in blockchain smart contracts?

Variable packing is a technique to store multiple smaller variables together in a single storage slot to save space and reduce gas costs.

beginner

Why is variable packing important in blockchain development?

Because storage operations are expensive in blockchain, packing variables reduces storage slots used, lowering gas fees and improving contract efficiency.

intermediate

Which data types can be packed together in a single storage slot?

Smaller data types like uint8, bool, and bytes1 can be packed together if their total size fits within 32 bytes (256 bits).

intermediate

How does Solidity store variables in storage slots when using variable packing?

Solidity stores variables sequentially in 32-byte slots. Smaller variables declared consecutively are packed tightly into one slot if they fit.

intermediate

What happens if variables exceed the 32-byte storage slot size during packing?

If variables together exceed 32 bytes, Solidity places the extra variables in the next storage slot, so packing only works within slot size limits.

What is the main benefit of variable packing in blockchain smart contracts?

A Reduces gas costs by saving storage space

B Makes code run faster on the CPU

C Increases contract size

D Improves user interface design

Variable packing reduces the number of storage slots used, which lowers gas costs.

Which of these data types can be packed together in one storage slot?

A string, uint256, address

B uint8, bool, bytes1

C uint256, uint256, uint256

D mapping, array, struct

Small fixed-size types like uint8, bool, and bytes1 can be packed together if they fit in 32 bytes.

How many bytes does one storage slot hold in Solidity?

A 32 bytes

B 128 bytes

C 64 bytes

D 16 bytes

Each storage slot in Solidity holds 32 bytes (256 bits).

What happens if packed variables exceed the 32-byte slot size?

A They are truncated

B They cause a compile error

C Extra variables go to the next storage slot

D They are compressed automatically

Variables exceeding the slot size are stored in the next slot.

Which of these is NOT a benefit of variable packing?

A Lower gas fees

B Reduced storage usage

C More efficient contract storage

D Faster transaction confirmation

Variable packing reduces storage and gas costs but does not directly speed up transaction confirmation.

Explain variable packing and why it matters in blockchain smart contracts.

Think about how storing many small variables together helps save money.

Describe how Solidity packs variables into storage slots and what limits this packing.

Imagine fitting small boxes into a bigger box without overflowing.