Example of Differences in Data Locations When Creating New Variables (Storage -> Storage vs Storage -> Memory)

Demo.sol

pragma solidity ^0.8.0;

contract Demo{
    event log(string data);
    string public d= "This is a variable";
    string public mv = "changed";
    string public mv2 = "changed2";
    constructor () {
        string storage x = d;
        string storage y = x; // Change this to: string memory y = x;
        emit log(x);
        emit log(y);
        d = mv;
        emit log(x);
        emit log(y);
        y = mv2;
        emit log(x);
        emit log(y);
    }
}