Solidity Solidity Interfaces, ABIs, and Events

Question 1

What is an interface in Solidity and what restrictions does it have?

Accepted Answer

A contract-like definition with only function signatures and no implementation, state variables, or constructors

Answer

A contract that can only emit events and read storage

Answer

An abstract contract that inherits from multiple parents

Answer

A special file format for ABI definitions

Question 2

What is the Solidity ABI (Application Binary Interface) used for?

Accepted Answer

It defines how to encode/decode function calls and return values between contracts and external callers

Answer

It is the compiled bytecode that runs on the EVM

Answer

It is the storage layout of a contract's state variables

Answer

It defines the event signatures emitted by a contract

Question 3

How is a function selector computed in Solidity?

Accepted Answer

It is the first 4 bytes of the keccak256 hash of the function's signature string (e.g., 'transfer(address,uint256)')

Answer

It is the first 4 bytes of the function's bytecode

Answer

It is an incrementing counter assigned at compile time

Answer

It is the keccak256 hash of the function name only

Question 4

What does `abi.encode` do differently from `abi.encodePacked`?

Accepted Answer

abi.encode pads each value to 32 bytes with standard ABI encoding; abi.encodePacked concatenates values without padding

Answer

abi.encodePacked adds a length prefix while abi.encode does not

Answer

abi.encode is only for external calls; abi.encodePacked is only for hashing

Answer

They are identical in behavior

Question 5

What is the risk of hash collisions when using `abi.encodePacked` with multiple dynamic types?

Accepted Answer

Two different sets of inputs can produce the same packed encoding (e.g., ['aa','b'] and ['a','ab'])

Answer

Packed encoding truncates values longer than 32 bytes

Answer

Dynamic types cause abi.encodePacked to revert

Answer

Hashes from encodePacked expire after one block

Question 6

What does `abi.decode` do in Solidity?

Accepted Answer

It decodes ABI-encoded bytes back into Solidity types, used for parsing return data from low-level calls

Answer

It validates that calldata is correctly formatted before execution

Answer

It converts bytecode back to Solidity source code

Answer

It decodes Base64-encoded metadata URIs