Mapping

定义

• mapping(address => uint) public ethBals;

• mapping(address => mapping(address => uint)) public coinBals;

操作:

• 赋值: ethBals[addr] = v;

• 修改: ethBals[addr] += v;

• 取值: ethBals[addr];

• 删除: delete ethBals[addr];

思考: 如何实现可循环 Mapping ?