Understanding the ABI — Key concepts

Function signaturekeccak256("transfer(address,uint256)") → first 4 bytes = selector. Parameter order and types must match exactly.

Trusted third parties are security holes.

— Nick Szabo

EncodingABI encoding packs static types (uint256, address, bool) and offsets to dynamic types (strings, bytes, arrays). Misordered args = bad decode.

OverloadsTwo functions can share a name with different types; their selectors differ. Overuse can confuse integrators—avoid unless necessary.

EventsEvent signature is keccak of the event declaration; indexed params go to topics, others to data. Changing any type changes the signature.

// Signature → selector (4 bytes)
// transfer(address,uint256) → 0xa9059cbb
function transfer(address to, uint256 amount) external returns (bool);