Define functions and events

While defining an interface is not a necessary step, functions and events can be defined in Huff contracts for two purposes: To be used as arguments for the __FUNC_SIG and __EVENT_HASH builtins, and to generate a Solidity Interface / Contract ABI.

Functions can be of type view, pure, payable or nonpayable, and function interfaces should only be defined for externally facing functions.

Events can contain indexed and non-indexed values.

Parameters of functions, events and errors can be tuples, the ABI form of a Solidity struct, written as their component types in parentheses. Component names are optional, and a tuple can be nested or used as an array. The selector uses the canonical type, so swap((address maker, uint256 amount) order) has the selector of swap((address,uint256)), the same as a Solidity function taking a struct with those fields. Each tuple becomes a struct in the interface -g generates.

Example

Define a function:

#define function testFunction(uint256, bytes32) view returns (bytes memory)

Define a function that takes a struct and returns an array of them:

#define function fill((address maker, uint256 amount) order) nonpayable returns ((address,uint256)[])

Define an event:

#define event TestEvent(address indexed, uint256)

Define an error that takes a struct:

#define error InvalidOrder((address maker, uint256 amount) order)