嘗試創建抽象合約的實例

pragma solidity ^0.5.0;
import 'https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/math/SafeMath.sol';

contract SubToken{
   mapping(address => uint) balances;

   string  symbol;
   string  name;
   uint8  decimals;
   uint  totalSupply; 

   using SafeMath for uint;

   //subtoken_struct public sub_tokens;

   //mapping(address  => subtoken_struct) public mySubTokens ;

   address contract_address; 

   constructor(string memory _name,string memory _symbol,uint8 _decimals,uint256 _totalSupply)  public{ 
       name = _name; 
       symbol = _symbol; 
       decimals=_decimals; 
       totalSupply = _totalSupply; 
       balances[msg.sender]=_totalSupply; 
   } 
   //function totalSupply() public view returns (uint);
   //function balanceOf(address tokenOwner) public view returns (uint balance);
   //function allowance(address tokenOwner, address spender) public view returns (uint remaining);
   //function transfer(address to, uint tokens) public returns (bool success) ;
   //function approve(address spender, uint tokens) public returns (bool success);
   function transferFrom(address from, address to, uint tokens) public returns (bool success);

   event Transfer(address indexed from, address indexed to, uint tokens);
   event Approval(address indexed tokenOwner, address indexed spender, uint tokens);

}
contract MainContrat {
   mapping(address => uint) balances;

   mapping(address => mapping(address => uint)) allowed;
   mapping(address => address[]) public created;

   mapping(address => SubToken) public tokenlist;

   address[] public contracts;
   address owner = msg.sender;

   using SafeMath for uint;

   address contract_address;

   function createNewContract(string memory _name,string memory _symbol,uint8 _decimals,uint256 _totalSupply) public returns(address newAddres){ 
       SubToken mc = new SubToken(_name,_symbol,_decimals,_totalSupply); 
       created[msg.sender].push(address(mc)); 
       contracts.push(address(mc)); 
       return address(mc); 
   }

   function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
       emit Transfer(_from, _to, _value);
       return true;
   }
   event Transfer(address indexed _from, address indexed _to, uint256 _value);
   event Approval(address indexed _owner, address indexed _spender, uint256 _value);

}

嘿伙計們，我有一份主契約，並且有一個 creteContract 功能。這個函式創建一個新的子令牌，所以我像介面一樣使用 subToken。

當我編譯我的契約時，我收到了這樣的錯誤：

TypeError：試圖創建一個抽象合約的實例。SubToken mc = new SubToken(_name,_symbol,_decimals,_totalSupply); ^———-^ browser/crtcont7.sol:32:5: 缺少實現：函式 transferFrom(address from, address to, uint tokens) public return (bool success); ^————————————————- —————————————————-^

pragma solidity ^0.5.0; 
import 'https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/math/SafeMath.sol'; 

contract SubToken{ 
   mapping(address => uint) balances; 

   string  symbol; 
   string  name; 
   uint8  decimals; 
   uint  totalSupply;  

   using SafeMath for uint; 

   address contract_address;  

   constructor(string memory _name,string memory _symbol,uint8 _decimals,uint256 _totalSupply)  public{  
       name = _name;  
       symbol = _symbol;  
       decimals=_decimals;  
       totalSupply = _totalSupply;  
       balances[msg.sender]=_totalSupply;  
   }  

   //function transferFrom(address from, address to, uint tokens) public returns (bool success); 
   //function allowance(address tokenOwner, address spender) public view returns (uint remaining);  
   //function transfer(address to, uint tokens) public returns (bool success) ;  
   //function approve(address spender, uint tokens) public returns (bool success);  
   //function transferFrom(address from, address to, uint tokens) public returns (bool success);  

   event Transfer(address indexed from, address indexed to, uint tokens); 
   event Approval(address indexed tokenOwner, address indexed spender, uint tokens); 

} 
contract MainContract { 
   mapping(address => uint) balances; 

   mapping(address => mapping(address => uint)) allowed; 
   mapping(address => address[]) public created; 

   mapping(address => SubToken) public tokenlist; 

   address[] public contracts; 
   address owner = msg.sender; 

   using SafeMath for uint; 

   address contract_address; 
   /* 

   function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) { 
       emit Transfer(_from, _to, _value); 
       return true; 
   } 
   */ 
   function createNewContract(string memory _name,string memory _symbol,uint8 _decimals,uint256 _totalSupply) public returns(address){  
       SubToken st = new SubToken(_name,_symbol,_decimals,_totalSupply); 
        //st = new SubToken();  
       created[msg.sender].push(address(st));  
       contracts.push(address(st));  
       //return address(mc);  
   }  
   event Transfer(address indexed _from, address indexed _to, uint256 _value); 
   event Approval(address indexed _owner, address indexed _spender, uint256 _value); 

} 

您可以查看OpenZeppelin Contracts ERC20 代幣文件，看看這是否滿足您對 ERC20 代幣的需求。您可能還想使用OpenZeppelin IERC20 介面。

請注意，您應該只使用在官方版本中發布的 OpenZeppelin 程式碼，因此在使用 Remix 時您應該在導入中包含版本標記，或者您可以查看入門指南以獲取有關如何設置開發環境的資訊。

import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v2.3.0/contracts/math/SafeMath.sol";

您還可以在社區論壇中詢問有關如何使用 OpenZeppelin 合約的問題

披露：我是 OpenZeppelin 的社區經理

引用自：https://ethereum.stackexchange.com/questions/73611