Solidity Cheat Sheet Lesson

This cheat sheet is for your future reference. It may seem long but don’t worry, you don’t need to know these 🙂 You can use this sheet for quick look ups, or simply referencing the syntax for your development. If you want to know more, you can always check the official documentation: Cheatsheet — Solidity 0.8.21 documentation

1. Comments

Comments are used to annotate the code to make it easier to understand. They are ignored by the Solidity compiler.

Single-line comments: Use // to comment out a single line.
Multi-line comments: Use /* */ to comment out multiple lines.

// This is a single-line comment
/* This is a multi-line comment
   that spans several lines */

2. Pragma Directive

The pragma directive helps to lock the Solidity compiler version for your smart contract. This ensures that your contract will only compile with a compatible compiler.

pragma solidity ^0.8.0;

3. Import

The import statement is used to import code from other Solidity files. This is useful for code reusability and separation of concerns.

import "./SomeContract.sol";

4. Data Types

Solidity supports various data types:

uint: Unsigned integers, cannot be negative.
int: Signed integers, can be negative.
bool: Boolean, true or false.
address: Ethereum address.
bytes: Fixed-size byte arrays.
string: Dynamic-size string.

uint256 x = 42;
bool isTrue = true;
address user = msg.sender;

5. Enums

Enums help in creating custom types with a range of predefined constants, making code more readable and less error-prone.

enum State { Created, Locked, Inactive }
State public state = State.Created;

6. Structs

Structs allow you to create complex data types that group variables under a single name.

struct Person {
    string name;
    uint age;
}
Person public person = Person("Alice", 30);

7. Arrays

Arrays are data structures that can hold more than one value at a time. They can be fixed-size or dynamic.

uint[] public numbers = [1, 2, 3];

8. Mappings

Mappings are key-value stores that allow you to link one data type to another.

mapping(address => uint) public balances;

9. Functions

Functions are the building blocks of a Solidity contract. They define executable code and can read and modify contract state.

function add(uint x, uint y) public pure returns (uint) {
    return x + y;
}

10. Function Modifiers

Modifiers are reusable pieces of code that can change the behavior of functions. They are often used for access control.

modifier onlyOwner() {
    require(msg.sender == owner, "Not the owner");
    _;
}

11. Events

Events provide a logging mechanism for the blockchain. They are crucial for frontend applications to "listen" to changes in smart contracts.

event LogData(uint indexed data);

emit LogData(42);

12. Error Handling

Solidity uses require, assert, and revert for error handling:

require: Used for validating inputs and conditions. Consumes less gas.
assert: Used for internal errors.
revert: Similar to require but allows you to revert complex operations.

require(x > 0, "x must be greater than 0");

13. Inheritance

Inheritance allows a contract to acquire properties and behavior (i.e., state variables and functions) of a parent contract.

contract Child is Parent {
    // code
}

14. Interfaces

Interfaces define a contract's external functions and enable the interaction between different contracts.

interface IERC20 {
    function transfer(address to, uint256 value) external returns (bool);
}

15. Libraries

Libraries are reusable pieces of code that can be called from within your contracts. They are deployed only once at a specific address and linked to your contract.

using SafeMath for uint;

uint x = y.add(z);

16. Storage and Memory

Storage: Persistent data storage that forms the contract state. Changes are very costly in terms of gas.
Memory: Temporary data storage. It's erased between external function calls and is cheaper to use than storage.

uint[] storage myArray;
uint[] memory tempArray;

17. Payable

The payable keyword allows a function to receive Ether.

function deposit() public payable {
    // code
}

18. Fallback and Receive Functions

These functions are executed when a contract receives Ether without a function being called.

Fallback: A default function marked with fallback.
Receive: Explicit function to receive Ether, must be marked external payable.

fallback() external payable {
    // code
}

receive() external payable {
    // code
}

19. Constructor

A constructor is a special function that gets executed only once when the contract is deployed.

constructor() {
    owner = msg.sender;
}

20. Visibility

public: Accessible from this and other contracts.
private: Accessible only from this contract.
internal: Like private but also accessible in derived contracts.
external: Only accessible from other contracts.

uint public x;
uint private y;

21. View and Pure Functions

view: Functions that read the state but don't modify it.
pure: Functions that neither read nor modify the state.

function getView() public view returns (uint) {
    return x;
}

function getPure() public pure returns (uint) {
    return 42;
}

Solidity Fundamentals