## Summary

I make a solidity code explainer.

## Example

### Contract

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17  // SPDX-License-Identifier: MIT pragma solidity >= 0.4.22 < 0.8.5; contract Migrations { address public owner = msg.sender; uint public last_completed_migration[<0;29;7M; modifier restricted() { require(msg.sender == owner, "This function is restricted to the contract's owner"); _; } function setCompleted(uint completed) public restricted { last_completed_migration = completed; } }

### Explanation

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29  We declare a new contract called Migrations. This contract will be an abstract contract that we'll use to store the version number of our smart contracts. We'll use this contract to keep track of which version of our smart contracts we've deployed to the blockchain. We declare a state variable called last_completed_migration that will store the version number of the smart contract that we've deployed to the blockchain. We also declare a modifier that will restrict access to the setCompleted function to the owner of the contract. This is a way to prevent other people from modifying the state variable. We create a function called setCompleted that will set the value of the state variable last_completed_migration to the value passed in as an argument. We restrict access to this function by using the modifier restricted.

## Prompt

pf-explain-solidity-code/1
http://github.com/semiosis/prompts/blob/master/prompts/explain-solidity-code-1.prompt
  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65  task: "explain solidity code" doc: "Given some solidity code, explain it" prompt-version: 1 prompt: |+ Solidity explanations. Code example 1 pragma solidity 0.4.2; contract Election { // Read/write candidate string public candidate; // Constructor function Election () public { candidate = "Candidate 1"; } } Explanation of 1 Let me explain the above code. We start by declaring the solidity version with the pragma solidity statement. Next, we declare the smart contract with the "contract" keyword, followed by the contract name. Next, we declare a state variable that will store the value of the candidate name. State variables allow us to write data to the blockchain. We have declared that this variable will be a string, and we have set its visibility to public. Because it is public, solidity will give us a getter function for free that will allow us to access this value outside of our contract. We'll see that in action later in the console! Then, we create a constructor function that will get called whenever we deploy the smart contract to the blockchain. This is where we'll set the value of the candidate state variable that will get stored to the blockchain upon migration. Notice that the constructor function has the same name as the smart contract. This is how Solidity knows that the function is a constructor. Here is some new code: Code example 2 Explanation of 2 Let me also explain this code. engine: "OpenAI Codex" temperature: 0.3 max-generated-tokens: prompt-length top-p: 1.0 stop-sequences: - "" cache: on vars: - "solidity code" examples: - |+ // SPDX-License-Identifier: MIT pragma solidity >= 0.4.22 < 0.8.5; contract Migrations { address public owner = msg.sender; uint public last_completed_migration; modifier restricted() { require(msg.sender == owner, "This function is restricted to the contract's owner"); _; } function setCompleted(uint completed) public restricted { last_completed_migration = completed; } } info: on postprocessor: chomp | pen-str remove-starting-and-trailing-whitespace | pen-pretty-paragraph external-related: "https://www.dappuniversity.com/articles/the-ultimate-ethereum-dapp-tutorial/"

## Let’s try on some openzeppelin contracts

### contracts › access › Ownable.sol

Contract
https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/access/Ownable.sol
  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75  // SPDX-License-Identifier: MIT pragma solidity ^0.8.0; import "../utils/Context.sol"; /** * @dev Contract module which provides a basic access control mechanism, where * there is an account (an owner) that can be granted exclusive access to * specific functions. * * By default, the owner account will be the one that deploys the contract. This * can later be changed with {transferOwnership}. * * This module is used through inheritance. It will make available the modifier * onlyOwner, which can be applied to your functions to restrict their use to * the owner. */ abstract contract Ownable is Context { address private _owner; event OwnershipTransferred(address indexed previousOwner, address indexed newOwner); /** * @dev Initializes the contract setting the deployer as the initial owner. */ constructor() { _transferOwnership(_msgSender()); } /** * @dev Returns the address of the current owner. */ function owner() public view virtual returns (address) { return _owner; } /** * @dev Throws if called by any account other than the owner. */ modifier onlyOwner() { require(owner() == _msgSender(), "Ownable: caller is not the owner"); _; } /** * @dev Leaves the contract without owner. It will not be possible to call * onlyOwner functions anymore. Can only be called by the current owner. * * NOTE: Renouncing ownership will leave the contract without an owner, * thereby removing any functionality that is only available to the owner. */ function renounceOwnership() public virtual onlyOwner { _transferOwnership(address(0)); } /** * @dev Transfers ownership of the contract to a new account (newOwner). * Can only be called by the current owner. */ function transferOwnership(address newOwner) public virtual onlyOwner { require(newOwner != address(0), "Ownable: new owner is the zero address"); _transferOwnership(newOwner); } /** * @dev Transfers ownership of the contract to a new account (newOwner). * Internal function without access restriction. */ function _transferOwnership(address newOwner) internal virtual { address oldOwner = _owner; _owner = newOwner; emit OwnershipTransferred(oldOwner, newOwner); } }

### Explanations

1

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30  We start by importing the Context contract from the utils folder. This contract will give us access to the _msgSender() function, which will return the address of the account that called the function. We then declare the abstract contract Ownable, which will allow us to use the access modifiers onlyOwner. The constructor function is where we set the owner of the contract to the account that deployed it. This is done by calling the _transferOwnership() function, which is an internal function that will change the owner of the contract. The onlyOwner modifier will make sure that only the owner of the contract can call the function. The renounceOwnership function will make the contract ownerless. The transferOwnership function will change the owner of the contract to a new account.

2

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44  We start by importing the Context smart contract. This is a library that we'll use to make sure that the owner of the contract is the one who is calling it. We can do this by using the _msgSender() function. Next, we declare the contract as an abstract contract. This means that it will be an abstract class that cannot be instantiated. We do this with the "abstract" keyword. Then, we declare the constructor function. This is the only function that will be called when the contract is instantiated. We use the constructor keyword to declare it. Next, we declare the owner state variable. This is the only state variable that will be stored on the blockchain. It will store the address of the owner of the contract. Then, we declare the event that will be called when the owner is changed. This is a function that is called when an event is emitted. Finally, we declare the onlyOwner modifier. This is a modifier that is used to restrict the use of the function to the owner of the contract.

3

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49  We start by importing the Context smart contract. This is a library of code that we'll be using in our own smart contract. We'll be using it to restrict access to the contract to only the owner. Next, we declare the abstract contract that we'll be inheriting from. This is a contract that we'll be using as a base for our own smart contract. We'll be using it to restrict access to the contract to only the owner. The constructor function is where we'll set the owner of the contract. We'll be using the _transferOwnership function to set the owner of the contract. This function is an internal function that is used by the contract to change the owner of the contract. We'll see how to use it later in the console. The onlyOwner modifier is a modifier that restricts access to the function to only the owner of the contract. We'll use this modifier in our functions to restrict access to the contract to only the owner. The renounceOwnership function is used to remove the owner of the contract. It can only be called by the owner of the contract. The transferOwnership function is used to change the owner of the contract. It can only be called by the owner of the contract.

4

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94  This is the same code as the first example, except that it is abstract. This means that it will not be directly deployed to the blockchain. Instead, it will be used as a base class to create a new smart contract. This is useful for creating contracts that are based on a common base contract. We start by declaring the solidity version with the pragma solidity statement. Next, we declare the smart contract with the "contract" keyword, followed by the contract name. Next, we declare a state variable that will store the value of the candidate name. State variables allow us to write data to the blockchain. We have declared that this variable will be a string, and we have set its visibility to public. Because it is public, solidity will give us a getter function for free that will allow us to access this value outside of our contract. We'll see that in action later in the console! Then, we create a constructor function that will get called whenever we deploy the smart contract to the blockchain. This is where we'll set the value of the candidate state variable that will get stored to the blockchain upon migration. Notice that the constructor function has the same name as the smart contract. This is how Solidity knows that the function is a constructor. We also declare an event called OwnershipTransferred. This event will be emitted whenever ownership of the contract changes. This is useful for tracking changes in ownership. Next, we declare a modifier that will restrict access to the contract's functions. This modifier is called onlyOwner. It will make sure that only the owner of the contract can call the function. Finally, we declare a function called owner. This function will return the address of the owner of the contract. Then, we declare a function called onlyOwner. This function will throw an exception if it is called by anyone other than the owner of the contract. Next, we declare a function called renounceOwnership. This function will leave the contract without an owner. It will not be possible to call onlyOwner functions anymore. Can only be called by the current owner. Finally, we declare a function called transferOwnership. This function will transfer the ownership of the contract to a new account. Can only be called by the current owner.

5

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33  We start by declaring the solidity version with the pragma solidity statement. Next, we import the Context contract, which is a smart contract that we'll use to store the owner of the contract. This is a good practice to follow, as it will make it easier to migrate to newer versions of solidity. Then, we declare the abstract Ownable contract, which is a smart contract that we'll use to restrict access to functions. It will also give us a constructor function, which will allow us to set the owner of the contract. The constructor function will set the owner of the contract to the address of the account that deploys the contract. The onlyOwner modifier will restrict the access to the function to the owner of the contract. The renounceOwnership function will make the contract ownerless. The transferOwnership function will transfer the ownership of the contract to a new account.