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。
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
版权属于：区块链中文技术社区 / 转载原创者
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