Bank Account — Case Study

A Swift Package implementation of a thread-safe bank account system that supports deposits, withdrawals, and transfers between accounts. This project demonstrates modern Swift concurrency patterns using actors to ensure data integrity in concurrent environments.

Features

• Deposits: Add funds to an account with validation
• Withdrawals: Remove funds with balance and fraud checks
• Transfers: Transfer funds between different accounts
• Thread Safety: Built using Swift actors to prevent data races
• Error Handling: Comprehensive error handling for various edge cases
• Fraud Detection: Built-in fraud alert system for large transactions

Requirements

• Swift 6.2 or later
• Xcode 15.0 or later (for development)

Installation

Swift Package Manager

Add the following to your Package.swift file:

dependencies: [
    .package(url: "https://github.com/yourusername/bank-account-case-study.git", from: "1.0.0")
]

Or add it through Xcode:

1. File → Add Package Dependencies
2. Enter the repository URL
3. Select the version you want to use

Usage

Creating a Bank Account

import BankSystemCore

let account = BankAccount(
    owner: "John Doe",
    accountNumber: "123456789",
    balance: 1000.0
)

Making a Deposit

try await account.deposit(500.0)

Making a Withdrawal

try await account.withdraw(200.0)

Transferring Funds

let sender = BankAccount(owner: "Alice", accountNumber: "111", balance: 1000.0)
let receiver = BankAccount(owner: "Bob", accountNumber: "222", balance: 500.0)

try await sender.transfer(to: receiver, amount: 300.0)

Error Handling

The BankAccount class defines several error types:

• insufficientFunds: Attempted withdrawal or transfer exceeds available balance
• invalidAmount: Amount is zero or negative
• sameAccountTransfer: Attempted to transfer to the same account
• fraudAlert: Transaction amount exceeds the fraud threshold (default: $5,000)

do {
    try await account.withdraw(10000.0)
} catch BankAccount.Error.insufficientFunds {
    print("Not enough funds")
} catch BankAccount.Error.fraudAlert {
    print("Transaction flagged for fraud review")
} catch {
    print("An error occurred: \(error)")
}

Testing

The project includes comprehensive test coverage using Swift Testing framework. Run the tests using:

swift test

Or in Xcode:

• Press Cmd + U to run all tests
• Or use the Test Navigator to run specific tests

Test Coverage

The test suite covers:

• Account initialization
• Successful deposits and withdrawals
• Invalid amount validation
• Insufficient funds scenarios
• Fraud detection
• Successful transfers
• Same account transfer prevention

Architecture

Swift Actors

The BankAccount is implemented as a Swift actor, which provides:

• Thread Safety: Automatic synchronization prevents data races
• Isolation: State is isolated and can only be accessed through async methods
• Concurrency: Safe concurrent access from multiple threads

Design Decisions

• Actor-based: Ensures thread-safe operations without manual locking
• Async/Await: Modern Swift concurrency for safe asynchronous operations
• Error Types: Custom error enum for clear error handling
• Fraud Threshold: Configurable static property for fraud detection limits

Project Structure

BankSystemCore/
├── Sources/
│   └── BankSystemCore/
│       └── BankAccount.swift      # Main bank account implementation
├── Tests/
│   └── BankSystemCoreTests/
│       └── BankAccountTests.swift # Test suite
└── Package.swift                   # Swift Package configuration

License

MIT © 2025 Juan Francisco Dorado Torres