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Solidity Fundamentals – The Counter Contract

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The Counter Contract

The Counter Contract

Lets make a contract that every time its called it increments by one.

Important side note, lets use this

import "hardhat/console.sol";














Lets create a counter contract















Contract Code
// SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.0;

import "hardhat/console.sol";

contract Counter {
    uint private counter;
    function count() public returns (uint) {
        counter++;
        console.log("counter", counter);
        return counter;
    }
}
Deploy Script
import _ from "@nomiclabs/hardhat-ethers";
import { ethers } from "hardhat";

async function deploy() {
    const C = await ethers.getContractFactory("Counter");
    const counter = await C.deploy();
    console.log(await counter.count());
}

deploy();
Output
{
  hash: '0xdd3ed28ae1706b0c602b148225a792723c7b6e8882a7ce46de9bb097965631a6',
  type: 2,
  accessList: [],
  blockHash: '0x773274e5ef072d8ff8c024b774af44c4ac04978c59552e783e215bc5dcc0ef73',
  blockNumber: 10,
  transactionIndex: 0,
  confirmations: 1,
  from: '0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266',
  gasPrice: BigNumber { _hex: '0x0fe0c2de', _isBigNumber: true },
  maxPriorityFeePerGas: BigNumber { _hex: '0x00', _isBigNumber: true },
  maxFeePerGas: BigNumber { _hex: '0x141876a0', _isBigNumber: true },
  gasLimit: BigNumber { _hex: '0xb8f8', _isBigNumber: true },
  to: '0x2279B7A0a67DB372996a5FaB50D91eAA73d2eBe6',
  value: BigNumber { _hex: '0x00', _isBigNumber: true },
  nonce: 9,
  data: '0x06661abd',
  r: '0x78300d5ce5a0f443153f4fb01fa352dba00d03a29b32edb428d510db81de9467',
  s: '0x77135829f88da53c7f318787bc202fad4ae5ab130baac89d5aec11b43fcc5a82',
  v: 1,
  creates: null,
  chainId: 31337,
  wait: [Function]
}
Ether chain output
  Contract call:       Counter#count
  Transaction:         0xb7df53fe40df541c52fac6e3cac0194e4e657d398c429490e52db986d56d8014
  From:                0xf39fd6e51aad88f6f4ce6ab8827279cfffb92266
  To:                  0x0165878a594ca255338adfa4d48449f69242eb8f
  Value:               0 ETH
  Gas used:            47352 of 47352
  Block #8:            0x617d3cdd8cfdbfc8ad50b94a85ebd67f35da73ff36a52d9a4fe869c860f7e741

  console.log:
    counter 1

eth_chainId
eth_getTransactionByHash














What Happened here?

We made a transaction, not a call. Therefore, sorry. No data.















Storage is extremely expensive

You altered state. You pay for it.















We are going to re-execute our deploy script

what is going to happen?















Two things that may have surprised you

  1. If we re-execute our deploy script, we keep seeing 1.
  2. If print the output, we get a bunch of non-sense.

Lets talk about each!















1. Why does it keep display 1?

Lets look at our script again and its output















2. What is with the output?

Well, we altered state, which required a eth_transaction. Which means you need to have several confirmations before its considered "set."















Rule of Thumb

You can only get data out from view or pure functions.

  1. NO MONEY
  2. NO MONEY
  3. NO TX

This only works with readonly functions.















The Read Only Functions

  • view functions are functions that do not change the contracts state.
  • pure cannot read or write state on the contract.

Since were here... Scopes

Lets break down these different meanings of public, private, internal, external

+------------+------------+-------------+--------------+--------------+
|            |   public   |   private   |   internal   |   external   |
+------------+------------+-------------+--------------+--------------+
|  Contract  |    yes     |     yes     |     yes      |      no      |
|  can call  |            |             |              |              |
+------------+------------+-------------+--------------+--------------+
| SubContract|    yes     |     no      |     yes      |      no      |
|  can call  |            |             |              |              |
+------------+------------+-------------+--------------+--------------+
|  Outside   |    yes     |     no      |     no       |      yes     |
|  can call  |            |             |              |              |
+------------+------------+-------------+--------------+--------------+

Lets rewrite our counter contract and separate it out.















Lets call that getCount function!

Lets update our deploy script.















Why BigNumber?















Whats the size of an int?















It depends is the only answer

  • JavaScript Number: 2**53 - 1
    • 9007199254740991.0
  • Rust: i32
  • Cpp: depends on arch or you can use uint32_t
  • Solidity: 256 bits - 32 bytes

Why BigNumber?

  • 256 bits > 2 ** 53 - 1
  • BigNumber allows for large decimal values.

Lets do an experiment

Lets return a smaller than 53 bit number!















Why?

Its not ethereum that is smart here, its ethersjs.















Lets make a small website that displays the count















That was a lot to take in

Questions?















I am not done here... Lets deploy this somewhere else..

In a rinkeby far far away... Rinkeby Faucet https://faucets.chain.link/rinkeby















That was AWESOME

Questions?