映射

映射其实就是字典，k-v 数据结构

定义方式

mapping(keyType => valueType)

映射操作: set、get、delete

• delete 操作仅仅只是将对应的值初始化
• get 操作获取一个不存在的 key 时，会返回初始化的数据
• mapping 不能直接迭代，需要借助其他数据结构进行迭代
• mapping 不能用于作为返回值

pragma solidity ^0.8.3;

contract Mapping {
    mapping(address => uint256) public balances;

    function setBalance(address _account, uint256 _balance) external {
        balances[_account] = _balance;
    }

    function getBalance(address _account) external view returns(uint256) {
        return balances[_account];
    }

    function addBalance(address _account,uint256 _amount) external {
        balances[_account] += _amount;
    }

    function deleteBalance(address _account) external {
        // 这里等价于 balances[_account] = 0;
        delete balances[_account];
    }
}

可迭代的 mapping

通过数组保存 Key 的值实现可遍历

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.3;

contract IterableMapping {
    mapping(address => uint) public balances;
    mapping(address => bool) public inserted;
    address[] public keys;

    function set(address _key, uint _val) external {
        balances[_key] = _val;
        if (!inserted[_key]) {
            inserted[_key] = true;
            keys.push(_key);
        }
    }

    function getSize() external view returns (uint) {
        return keys.length;
    }

    function first() external view returns (uint) {
        if (keys.length > 0) {
            return balances[keys[0]];
        }
        return 0;
    }

    function last() external view returns (uint) {
        if (keys.length > 0) {
            return balances[keys[keys.length - 1]];
        }
        return 0;
    }

    function get(uint _i) external view returns (uint) {
        if (keys.length > _i) {
            return balances[keys[_i]];
        }
        return 0;
    }
}