文件列表:

contracts/
scripts/
utils/
hardhat.config.js
helper-hardhat-config.js
package.json
yarn.lock

## Lesson 3: Functions and Modifiers in Solidity ### Objective: To understand how to write and use functions in Solidity, and to learn about function modifiers for enforcing certain conditions and managing access control in smart contracts. ### Part 1: Functions in Solidity ##### Function Declaration and Types: Understand the syntax for declaring functions. Different types of functions: public, private, internal, and external. ##### Return Values and Visibility: How to define return values for functions. Understand the implications of function visibility. ##### Function Modifiers: Usage of view, pure, and state-changing functions. ##### Function Parameters: Passing parameters to functions. Using memory and storage keywords for complex data types. ##### Example: Creating a Function solidity Copy code pragma solidity ^0.8.0; contract MyContract { uint public count = 0; function increment() public { count += 1; } function getCount() public view returns (uint) { return count; } } ### Part 2: Modifiers in Solidity ##### Understanding Modifiers: Purpose of modifiers in Solidity. Writing custom modifiers to enforce conditions. Common Use Cases: Restricting access to certain functions. Validating inputs or conditions before executing function logic. Example: Using a Modifier solidity Copy code pragma solidity ^0.8.0; contract MyContract { address public owner; constructor() { owner = msg.sender; } modifier onlyOwner() { require(msg.sender == owner, "Not the owner"); _; } function changeOwner(address newOwner) public onlyOwner { owner = newOwner; } } ### Assignments and Practical Exercises ##### Assignment 1: Research and write a brief explanation of how and why view and pure modifiers are used in Solidity functions. ##### Exercise 1: Create a smart contract with a few functions demonstrating different visibility levels (public, private, internal, external) and return values. ##### Exercise 2: Write a contract that includes a custom modifier. Use this modifier to restrict access to one of the contract's functions. ##### Token Wallet with Withdrawal Limits Use Case Overview: Implement a smart contract that acts as a wallet for a specific token. This contract would allow users to deposit, withdraw, and check their token balance, with daily withdrawal limits for security. #### Functions: depositTokens: A public function to deposit tokens into the wallet. withdrawTokens: An external function to withdraw a specified amount of tokens, adhering to daily limits. getBalance: A public view function to check the token balance of a user. Modifiers: withdrawalLimitCheck: A custom modifier to enforce the daily withdrawal limit per user. sufficientBalance: A modifier to ensure the user has enough tokens for withdrawal requests. These use cases involve various function types and custom modifiers, providing a comprehensive understanding of how these elements can be combined to build functional and secure smart contracts. You can further explore these ideas by considering aspects like security, efficiency, and user interaction within the smart contract ecosystem. This lesson will help you understand how to structure the logic within your smart contracts using functions and modifiers. These are key concepts in Solidity and are essential for writing secure and efficient smart contracts. Once you've completed this lesson, you'll have a deeper understanding of how to control access and enforce specific logic flows in your smart contracts.

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