Design Patterns - Facade Pattern

Intent
Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use.

Façade pattern is different from adapter pattern because façade simplifies a class structure while adapter keeps the same class structure.

The Façade pattern is a way to structure our API into subsystems to reduce ever growing size and complexity of interfaces of API.

Here is an example code:

#include <iostream>

// Subsystem 1
class SubSystemOne
{
public:
	void MethodOne(){ std::cout << "SubSystem 1" << std::endl; };
};

// Subsystem 2
class SubSystemTwo
{
public:
	void MethodTwo(){ std::cout << "SubSystem 2" << std::endl; };
};

// Subsystem 3 
class SubSystemThree
{
public:
	void MethodThree(){ std::cout << "SubSystem 3" << std::endl; }
};


// Facade
class Facade
{
public:
    Facade()
    {
	pOne = new SubSystemOne();
	pTwo = new SubSystemTwo();
	pThree = new SubSystemThree();
    }

    void MethodA()
    {
	std::cout << "Facade::MethodA" << std::endl;
	pOne->MethodOne();
	pTwo->MethodTwo();
    }

    void MethodB()
    {
	std::cout << "Facade::MethodB" << std::endl;
	pTwo->MethodTwo();
	pThree->MethodThree();
    }

private:
    SubSystemOne *pOne;
    SubSystemTwo *pTwo;
    SubSystemThree *pThree;
};

int main()
{
    Facade *pFacade = new Facade();

    pFacade->MethodA();
    pFacade->MethodB();

    return 0;
}

Output is:

Facade::MethodA
SubSystemOne: 1
SubSystem 2
Facade::MethodB
SubSystem 2
SubSystem 3

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