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Overview

The AddFiveStorage contract is a child contract that inherits from SimpleStorage. It demonstrates contract inheritance and function overriding in Solidity by modifying the behavior of the store() function to automatically add 5 to any stored value.

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Contract Details

  • License: MIT
  • Solidity Version: 0.8.30
  • Inherits: SimpleStorage
  • Imports: SimpleStorage from ./SimpleStorage.sol

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State Variables

This contract inherits all state variables from SimpleStorage, including:
  • myFavoriteNumber - A uint256 variable that stores the favorite number
  • listOfPeople - An array of Person structs
  • nameToNumber - A mapping from names to favorite numbers

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Functions

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store

function store(uint256 _favoriteNumber) public override
Stores a value in the contract, automatically adding 5 to the input value. Visibility: public State Mutability: Modifies state Modifier: override - This function overrides the parent SimpleStorage.store() function Parameters:
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_favoriteNumber
uint256
required
The base number to store. The actual stored value will be this number plus 5.
Description: This function overrides the parent contract’s store() function. Instead of storing the value directly, it adds 5 to the input before storing it in myFavoriteNumber. Behavior:
  • Input: _favoriteNumber
  • Stored: _favoriteNumber + 5
Example: 
AddFiveStorage storage = new AddFiveStorage();
storage.store(10);
uint256 value = storage.retrieve(); // Returns 15 (10 + 5)

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Inherited Functions

Since AddFiveStorage inherits from SimpleStorage, it also has access to these functions (unless overridden):
  • retrieve() - Returns the stored favorite number
  • addPerson(string memory _name, uint256 _favoriteNumber) - Adds a person to the list

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Complete Contract Code

// SPDX-License-Identifier: MIT
pragma solidity 0.8.30;

import {SimpleStorage} from "./SimpleStorage.sol";

contract AddFiveStorage is SimpleStorage {
    function store(uint256 _favoriteNumber) public override {
        myFavoriteNumber = _favoriteNumber + 5;
    }
}

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Key Concepts Demonstrated

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Inheritance

This contract uses the is keyword to inherit from SimpleStorage: 
contract AddFiveStorage is SimpleStorage
This means AddFiveStorage automatically receives all state variables and functions from its parent contract.

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Function Overriding

The store() function uses the override keyword to replace the parent contract’s implementation: 
function store(uint256 _favoriteNumber) public override
In Solidity 0.8.30, functions can be overridden even if the parent function is not explicitly marked as virtual. The override keyword indicates this function replaces the parent implementation.

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Direct State Variable Access

The overridden function directly accesses the inherited myFavoriteNumber state variable: 
myFavoriteNumber = _favoriteNumber + 5;

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Usage Examples

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Basic Usage

// Deploy the AddFiveStorage contract
AddFiveStorage addFive = new AddFiveStorage();

// Store a value (automatically adds 5)
addFive.store(20);

// Retrieve the value
uint256 storedValue = addFive.retrieve(); // Returns 25

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Using with StorageFactory

While AddFiveStorage can be used independently, it can also be deployed as part of a factory pattern similar to StorageFactory, demonstrating polymorphism in Solidity. 
// If StorageFactory were modified to accept different storage types
AddFiveStorage customStorage = new AddFiveStorage();
customStorage.store(100); // Stores 105

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