// SPDX-License-Identifier: MIT pragma solidity ^0.8.0; /** * @dev Provides tracking nonces for addresses. Nonces will only increment. */ abstract contract Nonces { /** * @dev The nonce used for an `account` is not the expected current nonce. */ error InvalidAccountNonce(address account, uint256 currentNonce); mapping(address account => uint256) private _nonces; /** * @dev Returns the next unused nonce for an address. */ function nonces(address owner) public view virtual returns (uint256) { return _nonces[owner]; } /** * @dev Consumes a nonce. * * Returns the current value and increments nonce. */ function _useNonce(address owner) internal virtual returns (uint256) { // For each account, the nonce has an initial value of 0, can only be incremented by one, and cannot be // decremented or reset. This guarantees that the nonce never overflows. unchecked { // It is important to do x++ and not ++x here. return _nonces[owner]++; } } /** * @dev Same as {_useNonce} but checking that `nonce` is the next valid for `owner`. */ function _useCheckedNonce(address owner, uint256 nonce) internal virtual { uint256 current = _useNonce(owner); if (nonce != current) { revert InvalidAccountNonce(owner, current); } } }