45. EIP-2612 permit (typed data)

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract Permit {
    bytes32 public immutable DOMAIN_SEPARATOR;
    // TODO PERMIT_TYPEHASH
    constructor() { DOMAIN_SEPARATOR = keccak256(abi.encode(keccak256("EIP712Domain"), block.chainid, address(this))); }
    function digest(address owner, address spender, uint256 value, uint256 nonce, uint256 deadline) external view returns (bytes32) {
        // TODO
    }
}