Solidity

Can be run using Remix, a browser-based IDE.

Code

Basics

// SPDX-License-Identifier: UNLICENSED
pragma solidity 0.8.7;

contract SimpleStorage {
    //public automatically creates getter function for you
    uint256 favNumber = 69;
    People public person = People({favouriteNumber: 2, name: "Gavin"});

    // mapping
    mapping(string => uint256) public nameToFavouriteNumber;

    // People type
    struct People {
        uint256 favouriteNumber;
        string name;
    }

    // People Array, called people - dynamic array
    People[] public people;

    // People[3] public people - Max of 3 in the array

    // can create your own getter function
    function retrieve() public view returns(uint256){
        return favNumber;
    }

    // view & pure functions don't require gas (pure functions don't allow viewing/ editing)
    // unless you call it within a function that requires gas
    // pure
    function purefn() public view returns(uint256){
        return favNumber;
    }

    function store(uint256 _favNumber) public {
        favNumber = _favNumber;
    }

    function addPerson(string memory _name, uint256 _favouriteNumber) public {
        People memory newPerson = People({favouriteNumber: _favouriteNumber, name: _name});
        people.push(newPerson);

        nameToFavouriteNumber[_name] = _favouriteNumber;
    }
}

EVM Overview

EVM (Eth virtual machine) can access and store information in 6 different places.

For special types (Array, Struct and Mapping), must declare explicitly.

1. Stack
2. Memory - temp vars that can be modified
3. Storage - permanent & can be modified
4. Calldata - temp vars that cannot be modified
5. Code
6. Logs