Solidity — 启用 ABIEncoderV2 以使用 Structs 作为函数参数

如果您一直在以太坊上进行开发，您就会知道无法将结构从合约传递到合约或从 web3 传递到合约的痛苦。在 Atra Blockchain Services，我们为用户自动创建和部署以太坊合约，这一限制直接影响了我们的数据存储服务 dTables。

现在，启用 ABIEncoderV2 后，您可以将结构类型从 web3 或其他合约传递给函数。在启用 ABIEncoderV2 的情况下编译合约时，编译后的 ABI 输出会发生一些变化。ABI JSON 现在将包含一种称为“元组”的新类型，当它遇到结构作为函数中的参数时。元组类型与属性“组件”配对，组件属性是一个包含 {name, type} 对象列表的数组。
下面是使用结构体作为输入参数的合约的 ABI 示例。注意类型和组件属性。
（GitHub code）

{
  "constant": false,
  "inputs": [{
    "components": [{
      "name": "text",
      "type": "string"
    }],
    "name": "recordData",
    "type": "tuple"
  }],
  "name": "Insert",
  "outputs": [{
    "name": "success",
    "type": "bool"
  }],
  "payable": false,
  "stateMutability": "nonpayable",
  "type": "function"
}

下面是一个使用新编码器的示例存储合约 （GitHub code）

pragma solidity ^0.5.3;
//注意此处
pragma experimental ABIEncoderV2;  //0.7.0 之前需添加支持
pragma abicoder v2; // 0.7.0 之后需要添加

contract storageContract {

  event Inserted(address _sender, address _recordId);
  event Updated(address _sender, address _recordId);
  event Deleted(address _sender, address _recordId);

  struct Data {
    string text;
  }
  struct Record {
    Data data;
    uint idListPointer;
  }

  mapping(address => Record) public Table;
  address[] public IdList;

  constructor() public {}

  // Check if recordId is in IdList, it's common for the record to be deleted and not by in the IdList anymore
  function Exists(address recordId) public view returns(bool exists) {
    if (IdList.length == 0) return false;
    return (IdList[Table[recordId].idListPointer] == recordId);
  }

  function GetLength() public view returns(uint count) {
    return IdList.length;
  }

  function GetByIndex(uint recordIndex) public view returns(address recordId, Data memory record) {
    require(recordIndex < IdList.length);
    return (IdList[recordIndex], Table[IdList[recordIndex]].data);
  }

  function GetById(address recordId) public view returns(uint index, Data memory record) {
    require(Exists(recordId));
    return (Table[recordId].idListPointer, Table[recordId].data);
  }

  function Insert(Data memory recordData) public returns(bool success) {
    address recordAddress = address(now);
    require(!Exists(recordAddress));
    Table[recordAddress].data = recordData;
    Table[recordAddress].idListPointer = IdList.push(recordAddress) - 1;
    emit Inserted(msg.sender, recordAddress);
    return true;
  }

  function Update(address recordId, Data memory recordData) public returns(bool success) {
    require(Exists(recordId));
    Table[recordId].data = recordData;
    emit Updated(msg.sender, recordId);
    return true;
  }

  // once a record has been deleted from the idList it can no longer be modified, but the memory remains
  // You can still pull deleted records if you hit the Table object directly, you will not be able to use GetByIndex or GetById
  function Delete(address recordId) public returns(bool success) {
    require(Exists(recordId));
    // get the record id to delete
    uint recordToDelete = Table[recordId].idListPointer;
    // set the last item in the id list to keep and move
    address keyToMove = IdList[IdList.length - 1];
    // replace the id of the deleted record with the one we want to keep i.e the last item
    IdList[recordToDelete] = keyToMove;
    // update the last record in the list to point to it's new position in the key list which is the old deleted records spot
    Table[keyToMove].idListPointer = recordToDelete;
    // remove the last element from the id list that holds the old pointer for the keep record
    IdList.length--;
    // emit event
    emit Deleted(msg.sender, recordId);
    return true;
  }

}

在函数参数中使用结构可以显着减少合约的混乱和复杂性，同时使它们交互起来更加愉快。

英文原文：https://medium.com/@dillonsvincent/solidity-enable-experimental-abiencoderv2-to-use-a-struct-as-function-parameter-27979603a879

注意

外部函数 不可以接受多维数组作为参数
如果原文件加入 pragma abicoder v2; 可以启用ABI v2版编码功能，这此功能可用。 （注：在 0.7.0 之前是使用pragma experimental ABIEncoderV2;）

内部函数 则不需要启用ABI v2 就接受多维数组作为参数。
参考自：https://learnblockchain.cn/docs/solidity/contracts.html