A bunch of example illustrating SOLID Principles

SOLID.swift

import Foundation

class Book {
    let name: String
    let authorName: String
    let year: Int
    let price: Double
    let isbn: String

    init(name: String, authorName: String, year: Int, price: Double, isbn: String) {
        self.name = name
        self.authorName = authorName
        self.year = year
        self.price = price
        self.isbn = isbn
    }
}

class Invoice {
    private(set) var book: Book
    private(set) var quantity: Int
    private(set) var discountRate: Double
    private(set) var taxRate: Double
    var total: Double { calculateTotal() }

    init(book: Book, quantity: Int, discountRate: Double, taxRate: Double) {
        self.book = book
        self.quantity = quantity
        self.discountRate = discountRate
        self.taxRate = taxRate
    }

    func calculateTotal() -> Double {
        let price: Double = ((book.price - book.price * discountRate) * Double(self.quantity));

        let priceWithTaxes: Double = price * (1 + taxRate);

        return priceWithTaxes;
    }
}

class InvoicePrinter {
    private let invoice: Invoice

    init(invoice: Invoice) {
        self.invoice = invoice
    }

    func printInvoice() {
        print(invoice.quantity, "x ", invoice.book.name, " " , invoice.book.price, " $");
        print("Discount Rate: ", invoice.discountRate);
        print("Tax Rate: ", invoice.taxRate);
        print("Total: ", invoice.total, " $");
    }
}

protocol InvoicePersistence {
    func save(invoice: Invoice)
}

class DatabasePersistence: InvoicePersistence {
    func save(invoice: Invoice) {
        // Save to DB
    }
}

class FilePersistence: InvoicePersistence {
    func save(invoice: Invoice) {
        // Save to file
    }
}

class PersistenceManager {
    let invoicePersistence: InvoicePersistence

    init(invoicePersistence: InvoicePersistence) {
        self.invoicePersistence = invoicePersistence;
    }
}

class Rectangle {
    fileprivate var width, height: Int;
    init(_ width: Int, _ height: Int) {
        self.width = width;
        self.height = height;
    }

    func getHeight() -> Int { height }

    func getWidth() -> Int { width }

    func getArea() -> Int { width * height }

    func setWidth(_ width: Int) {
        self.width = width;
    }

    func setHeight(_ height: Int) {
        self.height = height;
    }
}

class Square: Rectangle {
    init(_ size: Int) {
        super.init(size, size)
    }

    override func setWidth(_ width: Int) {
        super.setWidth(width)
        super.setHeight(width)
    }

    override func setHeight(_ height: Int) {
        super.setHeight(height)
        super.setWidth(height)
    }
}

class Test {

    static func getAreaTest(_ r: Rectangle) {
        let width = r.getWidth();
        r.setHeight(10);
        print("Expected area of ", (width * 10), ", got ", r.getArea());
    }

    static func main() {
        let rc = Rectangle(2, 3);
        getAreaTest(rc);

        let sq = Square(6);
        sq.setWidth(5);
        getAreaTest(sq);
    }
}

Test.main()
class Car {

}

protocol ParkingLot {

    func parkCar();    // Decrease empty spot count by 1
    func unparkCar(); // Increase empty spots by 1
    func getCapacity();    // Returns car capacity

}


protocol PaidParkingLot: ParkingLot {
    func calculateFee(_ car: Car) -> Double; // Returns the price based on number of hours
    func doPayment(_ car: Car);
}

protocol FreeParkingLot: ParkingLot {}

protocol HourlyFeeParkingLot: PaidParkingLot {}

protocol ConstantFeeParkingLot: PaidParkingLot {}