Allowance Wallet (Solidity Practice)

A beginner-friendly Solidity contract that demonstrates how one user can give another user permission to spend from their balance.
Built to learn how mapping, nested mapping, msg.sender, and require work together.

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🎯 Project Goal

To understand how to:

• Store user balances
• Set and manage allowances between users
• Use msg.sender to identify who is calling a function
• Apply require checks for validation

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🧱 Contract Overview

Contract Name: AllowanceWallet
Solidity Version: ^0.8.30

Variables

Variable	Type	Description
owner	address	The address that deployed the contract.
balances	mapping(address => uint256)	Tracks how much each user owns.
allowances	mapping(address => mapping(address => uint256))	Tracks how much one user allows another to spend.

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⚙️ Functions Overview

deposit(uint256 amount)

Adds balance to the caller’s own account.

setAllowance(address spender, uint256 amount)

Lets a user give another address permission to spend up to a certain amount from their balance.
Includes safety checks:

• Cannot give allowance to self.
• Allowance cannot exceed current balance.

spendFrom(address _owner, uint256 amount)

Allows a spender to spend part of the owner’s balance, if the owner gave them enough allowance.
Decreases both:

• The owner’s balance.
• The spender’s remaining allowance.

getBalance()

Returns the caller’s current balance.

getAllowance(address _owner, address spender)

Returns how much the spender can spend from the _owner's account.

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💡 Example Flow

1. Alice calls deposit(100) → Alice’s balance = 100
2. Alice calls setAllowance(Bob, 40) → Bob can spend 40 from Alice’s balance
3. Bob calls spendFrom(Alice, 25)
   • Alice’s balance = 75
   • Bob’s remaining allowance = 15

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🧪 Tools Used

• Remix IDE
• Solidity ^0.8.30

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🧠 What I Learned

• How to use nested mappings: mapping(address => mapping(address => uint256))
• How msg.sender identifies who is calling a function
• Why require is used for safety and validation
• Basic contract structure and data flow between users