Blockchain Solidity String的基本操作

refer to: 
https://ethereum.stackexchange.com/questions/30912/how-to-compare-strings-in-solidity

判断是否相同：

 17       if( keccak256(abi.encodePacked(result)) == keccak256(abi.encodePacked("")) ) {
 18         result = "buzz";
 19       }

链接：

string.concat(a, b);