> For the complete documentation index, see [llms.txt](https://andelf.gitbook.io/tron/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://andelf.gitbook.io/tron/smart-contract/use-solidity-like-a-professional.md).

# Use Solidity Like a Professional

## 标准 - The Standard

不要自己发明标准。用别人发明好的。

### TRC20, ERC20

最常见的代币合约，来自 ERC20.

### ERC223

兼容 ERC20.

定义了向合约转 token 的标准处理方式，要求合约支持 tokenFallback 调用，否则失败。（参数检查）

避免 ERC20 token 被发入黑洞地址（发往合约，如果该合约不能支持提token出来，那么就是黑洞）

### TRC721, ERC721

非同质化代币。例如以太猫。 NFT.

[ITRC721.sol](https://github.com/tronprotocol/sun-network/blob/develop/dapp-chain/contract/common/token/TRC721/ITRC721.sol)

### ERC1155

The Final Token Standard on Ethereum.

是 ERC20 和 ERC721 的结合体.。支持批量转账。

impl: [erc-1155](https://github.com/enjin/erc-1155)

### ERC1538

Future Proofing Smart Contracts and Tokens.

通过修改 delegate address 方式，使合约可以持续升级.

### ERC165

检查合约支持的接口。

```
function supportsInterface(bytes4 interfaceId) external view returns (bool)
```

### ERC1820

Contract interface Registry.

### ERC777

又一 ERC20 替代，兼容, 必须在 ERC1820 注册。方法较多。

### ERC1046

token(erc20) metadata uri. 链上管理 ERC20 token 的配置源信息。

但实际上是提供一个 URL 去下载一个固定格式的 JSON 文件。

1047 是其 metadata 格式 = ERC20Metadata

```
function tokenURI() external view returns (string);
```

Metadata 格式参考: [eip-1046](https://github.com/ethereum/EIPs/blob/master/EIPS/eip-1046.md)

## OpenZeppelin

合约实现的业界标杆。人类希望。

[OpenZeppelin/openzeppelin-contracts](https://github.com/OpenZeppelin/openzeppelin-contracts)

* AccessControl: role based access contrl
* Ownable: 提供 onlyOwner modifier, ownership 管理
* SafeMath/SignedSafeMath
* Pausable: 合约的紧急停止手段
* ReentrancyGuard: 防止函数被重入，重要的防攻击手段
* 及若干 TOKEN 实现

## 常见问题

### 合约代码升级

参考 ERC1538.

[tronprotocol/sun-network:dapp-chain/contract/common/delegatecallable/Delegatecallable.sol](https://github.com/tronprotocol/sun-network/blob/develop/dapp-chain/contract/common/delegatecallable/Delegatecallable.sol)

### 避免给合约转 Token

参考 ERC223.

### 如何编写安全的合约

* 先更改合约本地变量，再进行外部调用的风格
* 使用预言机机制获取外部参数时候，应该保存重要参数例如价格，与上一次做对比，波动过大时候暂停合约

### 2-step 随机数

波场缺乏链上随机变量，即所有TVM中可获取的外部变量均是可预测的。所以建议使用两步法产生随机变量。

概念验证代码（含合约和触发后端）

{% embed url="<https://gist.github.com/andelf/3f605596c19b1612cf7eaf8ed429e416>" %}


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