This EIP standardizes an interface containing a single function, multicall, allowing EOAs to call multiple functions of a smart contract in a single transaction, and revert all calls if any call fails.
Currently, in order to transfer several ERC-721 NFTs, one needs to submit a number of transactions equal to the number of NFTs being tranferred. This wastes users' funds by requiring them to pay 21000 gas fee for every NFT they transfer.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 and RFC 8174.
Contracts implementing this EIP must implement the following interface:
pragma solidity ^0.8.0;
interface IMulticall {
/// @notice Takes an array of abi-encoded call data, delegatecalls itself with each calldata, and returns the abi-encoded result
/// @dev Reverts if any delegatecall reverts
/// @param data The abi-encoded data
/// @returns results The abi-encoded return values
function multicall(bytes[] calldata data) external virtual returns (bytes[] memory results);
/// @notice OPTIONAL. Takes an array of abi-encoded call data, delegatecalls itself with each calldata, and returns the abi-encoded result
/// @dev Reverts if any delegatecall reverts
/// @param data The abi-encoded data
/// @param values The effective msg.values. These must add up to at most msg.value
/// @returns results The abi-encoded return values
function multicallPayable(bytes[] calldata data, uint256[] values) external payable virtual returns (bytes[] memory results);
}
multicallPayable is optional because it isn't always feasible to implement, due to the msg.value splitting.
This is compatible with most existing multicall functions.
The following JavaScript code, using the Ethers library, should atomically transfer amt units of an ERC-20 token to both addressA and addressB.
await token.multicall(await Promise.all([
token.interface.encodeFunctionData('transfer', [ addressA, amt ]),
token.interface.encodeFunctionData('transfer', [ addressB, amt ]),
]));
pragma solidity ^0.8.0;
/// Derived from OpenZeppelin's implementation
abstract contract Multicall is IMulticall {
function multicall(bytes[] calldata data) external virtual returns (bytes[] memory results) {
results = new bytes[](data.length);
for (uint256 i = 0; i < data.length; i++) {
(bool success, bytes memory returndata) = address(this).delegatecall(data);
require(success);
results[i] = returndata;
}
return results;
}
}
multicallPayable should only be used if the contract is able to support it. A naive attempt at implementing it could allow an attacker to call a payable function multiple times with the same ether.
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