Solidity-101-series

1. CRUD Operations in Solidity, Basic Smart Contract

• Let’s understand create, read, update, delete operations in solidity.
• Let’s understand the very basics of solidity and take things from here.
• Github code

contract  Blocktrain {
  uint256  public coins = 0;

  function  add() public {
     coins+=1;
  }

  function  subtract() public{
     coins-=1;
  }

  function  set(uint256  _coins) public{
     coins = _coins;
  }
}

2. Variable Data Types, Control Statements

• Variables Datatypes are similar to other languages.
• Some solidity specific variables include Address, Mapping(Hashmaps).
• Control statements are simply
  IF, ELSE IF, ELSE
• It works similarly to any other language
• Github code

3. Loops and Break Keyword

• Loops can be used for a variety of reasons. Think of making a blog website where you want to fetch all the posts? You iterate over the posts and store them in a data structure through a loop.

• Github code

4. Constructor, Require and Modifiers

• Constructor is the first function which gets triggered when the contract is deployed.

• One can setup some parameters like owner and other things.

• Require is a condition which needs to be satisfied else the code below the statement won’t be executed.

• Require takes in a particular condition and the error message which should be shown if the condition is not followed.

• Modifiers act as filters to the functions. Consider there is some condition which needs to be present before executing a function.

• You create a modifier using require keyword and add that modifier in front of every function which should follow that condition.

• You can create multiple modifiers for multiple reasons.

• One example could be some functions should only be called the owner of the contract ( owner is the address which deployed the contract )

• Github code

5. Creating your own coin with Open Zeppelin

• Open Zeppelin has this awesome tool Contract Wizard (https://wizard.openzeppelin.com/) which has a very simple UI to frame your basic smart contract.

• Click on the functions you require in your smart contract, they currently support all the popular protocols, ERC20, ERC1155, ERC721

• Github code

6. Built in keywords, msg, tx, block, ether units, time units

• Github code

• Above link is enough

7. Storage in Solidity

• Storage in solidity is done in 4 ways

• You can store some variables on the blockchain using “storage” keyword.

• Memory keyword is used to add a lifetime for the variables, like you just require the parameters of the function till the function is executing, you don’t require it later. Thus Memory keyword is used.

• Stack => All variables declared in a function are stored in a fixed size stack

• Calldata => Similar to Memory, this variables have a lifetime but are immutable

• Github code

8. Events in Solidity

• Events are basically a way to announce something in the outside world.

• You can use events for any interaction which happens on the smart contract.

• Something like an NFT got transferred from one address to other.

• These events can be later indexed from outside the smart contract and makes it easier to render things in the frontend.

• Events are used to keep a radar on smart contract interaction.

• Github code

9. Creating a Bank in Solidity

• Let’s create a bank

• The bank has multiple accounts, and each account has some variables to track.

• The functions are pretty simple, creating account, depositing and withdrawing.

• More functions can be added based on your imagination.

• Github code

10. Variables and Functions Visibility Deep Dive

• Variables and functions can be kept private as well as public as per required.

• You want your smart contract to be deterministic. And thus one should take care about which variables and functions are accessible where.

• Check the link below.

• Github code

11. Coding a Vault

• Let’s code a vault with a timer.

• In the Vault you can store your crypto and add a timer on top of it. You can’t withdraw the funds until the timer runs out.

• The code is pretty much similar to the bank we coded earlier but now we are dealing with time in solidity.

• Github code

12. Interaction with Multiple Smart Contracts

• Solidity is an Object oriented programming language and thus the OOPs concepts help us to manage the entire codebase in a neat manner.

• You can keep different contracts in multiple files and import using the import keyword.

• You can also keep all the contracts in a single file.

• Github code

13. Handling errors in solidity

• Errors are handled using various checking mechanisms.

• Require is one of them

• Require is a condition which needs to be satisfied else the code below the statement won’t be executed.

• Require takes in a particular condition and the error message which should be shown if the condition is not followed.

• Assert is used when writing protocols as it should follow the conditions strictly.

• Revert is used to break the transaction then and there. Its not used as Require does the work.

• Github code

14. Creating a Smart Contract Factory

• You can create one smart contract to create multiple new smart contracts.

• Consider you are building a project which is a token launchpad where people can come in and launch their personal tokens.

• This situation calls for a smart contract to make more.

• It can be achieved by creating a parent contract and creating a new instance of the child contract whenever required.

• Github code

15. Sending ERC20 Token

• Whenever dealing with transfers, its mostly the transfer of the native token, for Ethereum, transfer function sends Eth, For Polygon it sends Matic etc.

• But we can also send any custom ERC20 token via just making a few tweaks.

• One needs to import ERC20 standard from open zeppelin

• And pass the contract address of the ERC20 token you want to transact with.

• Github code

16. Using Chain Link Data Feeds in Solidity

• The smart contract is immutable once its deployed.

• There might be cases where you require real time data in the smart contract like the current price of BTC or some API interaction.

• This is where oracles come in, oracles are decentralized way to get the external world facts in the smart contract.

• One of the leading oracles is Chainlink and they have a very easy documentation to get the data feeds on multiple chains.

• https://docs.chain.link/docs/using-chainlink-reference-contracts/

• Chainlink supports multiple chains on which you can get data feeds of multiple currencies.

• Github code