strings.sol

pragma solidity ^0.7.1;

contract C {
    function compare(string memory s1, string memory s2) public pure returns (bool) {
        return keccak256(abi.encodePacked(s1)) == keccak256(abi.encodePacked(s2));
    }
    
    function concatenate(string memory s1, string memory s2) public pure returns (string memory) {
        return string(abi.encodePacked(s1, s2));
    }
}