22映射

mapping

// SPDX-License-Identifier: MIT
pragma solidity 0.8.18;

contract Mapping{
    // 定义mapping
    mapping (address=>uint) public balances;
    mapping (address=> mapping (address=>bool)) public isFriend;

    function examples() external {
        // 赋值
        balances[msg.sender]=123;

        //get
        uint bal=balances[msg.sender];
        uint bal2=balances[address(0)];//不存在的值，返回默认值0

        //modify
        balances[msg.sender]+=456;

        //delete
        delete balances[msg.sender];//成功返回默认值0

        //嵌套map
        isFriend[msg.sender][address(this)]=true;//address(this)当前地址
    } 
}