[Solidity] 230221 study

Some contents of this article are based on Cryptozombies’s source code, based on GPL-3.0

Lesson 2

Chapter 1: Lesson Overview

Chapter 2: Mappings and Addresses

• Address: an address of account
  • it is a unique identifier that points to that account
• Mappings: a way of storing organizaed data in Solidity
  • mapping is key-value store

      mapping (address => uint) public accountBalance
    

Chapter 3: Msg.sender

• msg.sender: refers to the address of the person who called the current function
  • it gives the security of the Ethereum Blockchain
  • only way to modify someone else’s data is to steal the private key
  • mappingFunction[key] = value;

Chapter 4: Require

• In this trivial example, require is used to make each player can only call a function once
  • require(condition);
  • e.g., require(totalCount[msg.sender]<=2);

Chapter 5: Inheritance

• Make manageable contract, by organizing and making inheritance
• contract childContract is parentContract

Chapter 6: Import

• import "directory/of/file/fileName.sol";

Chapter 7: Storage & Memory

• Storage: permanently stored on the blockchain
• Memory: temporary stored, and erased between external functions

Chapter 8: Zombie DNA

• Keep examine and understand our structures and mappings

Chapter 9: More on Function Visibility

• private, public, internal, external
• internal: same w/ private, except that it is accesssible to contracts that inherit from this conctract
• external: same w/ public, except that it can only be called outside the contract

Chapter 10: What Do Zomibes Eat?

• interface: we need to define an interface, to talk to another contract that we don’t own
  • we decalre the funcion we want to interact with
  • we do not dfine the function bodies

Chapter 11: Using an Interface

Chapter 12: Hanling Multiple Return Values

• 리턴값 갯수와 순서를 맞춘다
• 순서대로 A, B, C 3개가 리턴되지만 C만 필요한 경우: (,,C) = multipleReturns();

Chapter 13: Bonus: Kitty Genes

• Remember keccak256(abi.encodePacked(value))