assembly let

let：在汇编代码块中定义的变量，在该代码块 外部是无法访问的
1.创建一个新的堆栈槽位
2.为变量保留该槽位
3.当到达代码块结束时自动销毁该槽位

// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.6.0 <0.9.0;
import "hardhat/console.sol";

contract Assembly1 {
    constructor(){     
    }

    function fun() public {
        uint256 a = 0;
        assembly {
            a := 2
        }
        console.log("a:",a);
    }

    function fun1(uint256 x,uint256 y) external view returns (uint256){
        uint256 result = 0;
        assembly {
            result := add(x, y)   // x + y
            mstore(0x0, result)       // 在内存中保存结果
            //return(0x0, 32)           // 从内存中返回32字节
        }
        console.log("fun1 result:",result);
        assembly {
            return (0x0,32)
        }
    }

    function fun2() external {
        uint256 x=0;
        uint256 y=0;
        uint256 z=0;
        uint256 n=0;
        string memory s = "a";
        assembly {
            x := 7 
            y := add(x, 3)
            z := add(keccak256(0x0, 0x20), div(64, 32)) 
            z := add(0x0, 0x20)
            let m  // 自动初始化为 m = 0
        }
        //console.log("x:%d,y:%d,z:%d,aaa:%s",x,y,z,s);
        console.logString(s);
        console.log("x:%d,y:%d,s:%s",x,y,s);
    }
}

const { expect } = require("chai");
const { ethers } = require("hardhat");

constractName = "Assembly1";

describe("contract", function () {
  it("test", async function () {
    const TestContract = await ethers.getContractFactory(constractName);
    const testContract = await TestContract.deploy();
    result = await testContract.fun();
    result = await testContract.fun1(1,2);
    console.log("result",result.toString());
    result = await testContract.fun2();
  });
});

  contract
a: 2
fun1 result: 3
result 3
a
x:7,y:10,s:a