Solidity 练习：映射

一、题目说明

映射就像 Python 中的哈希表或字典，它们对于快速有效的查找很有用。

二、任务列表

1. 编写一个 external 函数 get(address _addr)，返回 _addr 存储在 balances 中的余额。
2. 完成函数 set(address _addr, uint _val)，将 _addr 的余额设置为 _val，该函数必须是 external 的。
3. 完成函数 remove(address _addr)，删除 _addr 存储在 balances 中的余额，该函数必须是 external 的。

三、解答代码

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;

contract MappingBasic {
    // Mapping from address to uint used to store balance of addresses
    mapping(address => uint) public balances;

    // Nested mapping from address to address to bool
    // used to store if first address is a friend of second address
    mapping(address => mapping(address => bool)) public isFriend;

    function examples() external {
        // Insert
        balances[msg.sender] = 123;
        // Read
        uint bal = balances[msg.sender];
        // Update
        balances[msg.sender] += 456;
        // Delete
        delete balances[msg.sender];

        // msg.sender is a friend of this contract
        isFriend[msg.sender][address(this)] = true;
    }

    function get(address _addr) external view returns (uint) {
        return balances[_addr];
    }

    function set(address _addr, uint _val) external {
        balances[_addr] = _val;
    }

    function remove(address _addr) external {
        delete balances[_addr];
    }
}

四、参考资料

• Smart Contract Engineer Challenges (opens new window)