Ethereum Developer Ethereum Virtual Machine (EVM) and Gas Optimization 3

Question 1

Which Solidity technique saves gas by fitting multiple small variables into a single 32-byte storage slot?

Accepted Answer

Struct packing

Answer

Struct packing arranges variables so multiple small types (e.g., two uint128s) share one 32-byte slot, reducing the number of costly SSTORE and SLOAD operations.

Question 2

Why is reading function parameters from calldata cheaper than from memory in Solidity?

Accepted Answer

Calldata is read-only and avoids the gas cost of copying data into memory

Answer

Calldata is immutable transaction input that can be read directly without allocating or copying into memory, saving the gas cost of mstore and mload operations.

Question 3

Why can using `uint8` for local variables cost MORE gas than `uint256` in Solidity?

Accepted Answer

The EVM's 256-bit word size requires extra masking operations when using smaller types

Answer

Since the EVM natively operates on 256-bit words, using uint8 in local variables forces the compiler to add bit-masking operations, adding gas overhead.

Question 4

When are `view` functions completely free (zero gas cost) in Ethereum?

Accepted Answer

When called externally off-chain via eth_call (not as part of a transaction)

Answer

View functions cost zero gas when called off-chain via eth_call because they don't modify state and no transaction is broadcast to the network.

Question 5

Which gas optimization pattern moves expensive computation off-chain and uses on-chain verification only?

Accepted Answer

Merkle proofs and cryptographic verification

Answer

Merkle proofs allow a contract to verify membership in a large dataset with O(log n) on-chain hashing instead of storing and iterating the full dataset.

Ethereum Developer Practice Test

Ethereum Developer Practice Test

Ethereum Developer Ethereum Virtual Machine (EVM) and Gas Optimization 3