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 expansion

Answer

Memory mapping

Answer

Variable shadowing

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 stored on layer 2 networks

Answer

Calldata bypasses the EVM stack entirely

Answer

Calldata uses a compressed binary encoding

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

uint256 is stored more compactly in memory

Answer

uint8 is not directly supported by EVM arithmetic opcodes

Answer

uint256 enables better compiler optimizations

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

When called from within another contract

Answer

When the function accesses fewer than 5 storage slots

Answer

When declared inside a library contract

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

Lazy evaluation via storage flags

Answer

Storage sharding across contracts

Answer

Opcode batching via assembly

Question 6

How does using Solidity `library` contracts reduce deployment gas costs?

Accepted Answer

Library code is deployed once and reused via delegatecall, shrinking the calling contract's bytecode

Answer

Libraries are compiled to more efficient opcodes

Answer

Libraries bypass the EVM's gas metering

Answer

Libraries store their state in calldata instead of storage

Question 7

Why are Solidity events more gas-efficient than contract storage for recording historical data?

Accepted Answer

Events are stored in cheaper transaction logs (~8 gas/byte) rather than costly contract storage (~20,000 gas per slot)

Answer

Events are compressed automatically by the EVM before persisting

Answer

Events bypass block gas limits entirely

Answer

Events are stored off-chain and don't consume any gas