NFT合约解析（4）——Counters.sol——2021.5.19

一丶配置需求：

1.环境需求：WeBASE-Front

2.合约语言：Solidity >=0.6.0 <0.8.0

二丶Counters.sol

pragma solidity >=0.6.0 <0.8.0;

import "./SafeMath.sol";

library Counters {
   
   
    using SafeMath for uint256;

    struct Counter {
   
   
        uint256 _value; 
    }
    
    function current(Counter storage counter) internal view returns (uint256) {
   
   
        return counter._value;
    }

    function increment(