4.Constants

Immutable功能和constants很像，

区别是

immutable可以在部署合约的时候，调用构造函数，赋值

constants只能在写程序的时候写死

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.1;

contract Immutable {
    // coding convention to uppercase constant variables
    address public immutable MY_ADDRESS;
    uint public immutable MY_UINT;

    constructor(uint _myUint) {
        MY_ADDRESS = msg.sender;
        MY_UINT = _myUint;
    }
}