What is the facade design pattern?

Overview

The facade is a design pattern from software development that belongs to the category of structural patterns.

Purpose

This structural pattern gives a complicated set of classes, libraries, or frameworks a simple interface. While facade reduces the overall complexity of the program, it also aids in the consolidation of unneeded dependencies.

Benefits

It improves the readability and usefulness of a software library. It does so by offering a single simple API that hides interactions with more sophisticated components.
It gives more general functions, a context-specific interface.
It lowers the time complexity to learn how to use the subsystem effectively.

Structure

The façade pattern differs from the adapter pattern in that it simplifies a class structure while the adapter maintains the same structure.

// from https://medium.com/@andreaspoyias/design-patterns-a-quick-guide-to-facade-pattern-16e3d2f1bfb6
#include <iostream>
using namespace std;
class Waiter_Subsystem1
{
public:
  void writeOrder()   { cout << " Waiter writes client's order\n";}
  void sendToKitchen(){ cout << " Send order to kitchen\n";}
  void serveCustomer(){ cout << " Yeeei customer is served!!!\n";}
};
class Kitchen_Subsystem2
{
public:
    void prepareFood(){ cout << " Cook food\n";}
    void callWaiter() { cout << " Call Waiter\n";}
    void washDishes() { cout << " Wash the dishes\n";}
};
class Order_Facade
{
private:
    Waiter_Subsystem1 waiter;
    Kitchen_Subsystem2 kitchen;
public:
    void orderFood()
    {
        cout << "A series of interdependent calls on various subsystems:\n";
        waiter.writeOrder();
        waiter.sendToKitchen();
        kitchen.prepareFood();
        kitchen.callWaiter();
        waiter.serveCustomer();
        kitchen.washDishes();
    }
};
int main(int argc, char *argv[])
{
    // Simple for the client 
    // no need to know the order or the 
    // dependencies among various subsystems.
    //Rather than calling all different functions individually thanks to facade I only have 1 function...
    Order_Facade facade;
    facade.orderFood();
return 0;
}

Explanation

Lines 6 to 12: We create a class named Waiter_Subsystem1 with three methods: writeOrder(), sendToKitchen(), and serveCustomer().
Lines 13 to 19: We create a class named Kitchen_Subsystem2 with three methods: prepareFood(), callWaiter(), and washDishes().
Lines 21 to 37: We create a Order_Facade class with one method, orderFood(). We also create objects of Waiter_Subsystem1 and Kitchen_Subsystem2.
Lines 39 to 48: We create the object of the Order_Facade class and call the orderFood() function, which shows the output on the console accordingly.

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