Factory Class Pattern

Ch1156 (1999)

Is this how you do a factory pattern? Im curious to learn since it will make my design a little easier to scale. My code is still a work in progress but I just wanted to ask before i get too far.

#include <iostream>
#include <string>
#include <vector>
#include <random>
#include <chrono>
#include <algorithm>

std::mt19937 mt{ static_cast<unsigned int>(std::chrono::high_resolution_clock::now().time_since_epoch().count()) };

class Trait
{
	public:
		Trait(const std::string& name, const std::string& description) : 
			mName(name), mDescription(description)
		{}

		std::string GetName() const
		{
			return mName;
		}

		std::string GetDescription() const
		{
			return mDescription;
		}

	private:
		std::string mName{ "Trait Name" };
		std::string mDescription{ "Trait Description" };
};

class Effect
{
	public:
		Effect(const std::string& name, const std::string& description) : 
			mName(name), mDescription(description)
		{}

	private:
		std::string mName{ "Effects" };
		std::string mDescription{ "Effect Description" };
	};

	class BodyPart
	{
	public:
		BodyPart(const std::string& name, int hitPoints) : 
			mName(name), mHitPoints(hitPoints)
		{}

		std::string GetName() const
		{
			return mName;
		}

		int GetHitPoints() const
		{
			return mHitPoints;
		}

		void ApplyEffect(const Effect& effect)
		{
			mEffects.push_back(effect);
		}

	private:
		std::string mName{ "Body Part Name" };
		int mHitPoints{ 0 };

		std::vector<Effect> mEffects;
};

class Colonist
{
	public:
		Colonist(const std::string& firstName, const std::string& lastName, int biologicalAge, int chronologicalAge) :
			mFirstName(firstName), mLastName(lastName), mBiologicalAge(biologicalAge), mChronologicalAge(chronologicalAge)
		{}

		std::string GetFirstName() const
		{
			return mFirstName;
		}

		std::string GetLastName() const
		{
			return mLastName;
		}

		int GetBiologicalAge() const
		{
			return mBiologicalAge;
		}

		int GetChronologicalAge() const
		{
			return mChronologicalAge;
		}

		void AddTrait(const Trait& trait)
		{
			auto compare = [&trait](const Trait& a)
			{
				return a.GetName() == trait.GetName();
			};

			auto it = std::find_if(mTraits.begin(), mTraits.end(), compare);
			if (it == mTraits.end())
			{
				mTraits.push_back(trait);
			}
		}

		std::vector<Trait> GetTraits() const
		{
			return mTraits;
		}

		void AddBodyPart(const BodyPart& bodyPart)
		{
			auto compare = [&bodyPart](const BodyPart& a)
			{
				return a.GetName() == bodyPart.GetName();
			};

			auto it = std::find_if(mBodyParts.begin(), mBodyParts.end(), compare);
			if (it == mBodyParts.end())
			{
				mBodyParts.push_back(bodyPart);
			}
		}

		std::vector<BodyPart> GetBodyParts() const
		{
			return mBodyParts;
		}

	private:
		std::string mFirstName{ "Colonist First Name" };
		std::string mLastName{ "Colonist Last Name" };
		int mBiologicalAge{ 0 };
		int mChronologicalAge{ 0 };

		std::vector<Trait> mTraits;
		std::vector<BodyPart> mBodyParts;
};

class ColonistFactory 
{
	public:
		ColonistFactory(const std::vector<std::string>& firstNames, const std::vector<std::string>& lastNames, const std::vector<Trait>& traits, const std::vector<BodyPart>& bodyParts)
			: mFirstNames(firstNames), mLastNames(lastNames), mTraits(traits), mBodyParts(bodyParts)
		{}

		Colonist CreateRandomColonist() 
		{
			std::uniform_int_distribution<int> chooseRandomFirstName(0, mFirstNames.size() - 1);
			std::uniform_int_distribution<int> chooseRandomLastName(0, mLastNames.size() - 1);
			std::uniform_int_distribution<int> randomBiologicalAge(17, 100);
			std::uniform_int_distribution<int> randomChronologicalAge(0, 5447);
			std::uniform_int_distribution<int> randomTrait(0, mTraits.size() - 1);

			int firstNameIndex = chooseRandomFirstName(mt);
			int lastNameIndex = chooseRandomLastName(mt);
			int biologicalAge = randomBiologicalAge(mt);
			int chronologicalAge = randomChronologicalAge(mt);

			Colonist colonist(mFirstNames[firstNameIndex], mLastNames[lastNameIndex], biologicalAge, chronologicalAge);

			for (int i = 0; i < 3; ++i) 
			{
				colonist.AddTrait(mTraits[randomTrait(mt)]);
			}

			for (const auto& part : mBodyParts) 
			{
				colonist.AddBodyPart(part);
			}

			return colonist;
		}

	private:
		std::vector<std::string> mFirstNames;
		std::vector<std::string> mLastNames;
		std::vector<Trait> mTraits;
		std::vector<BodyPart> mBodyParts;
};


int main()
{
	// Initialization of data
	std::vector<std::string> firstNames
	{
		"Amanda",
		"Alex",
		"Alexis",
		"Alexa",
		"Angela",
		"Anna",
		"Brittany",
		"Blaine",
		"Brian",
		"Barney",
		"Betty",
		"Bob",
		"Chad",
		"Chelsea",
		"Chester",
		"Charlene",
		"David",
		"Donald",
		"Dorothy",
		"Destiny",
		"Dwayne"
	};

	std::vector<std::string> lastNames
	{
		"Hawkins",
		"Stevens",
		"Jacobson",
		"Karlson",
		"Benett",
		"Wilks",
		"Anders",
		"Peterson",
		"White",
		"Park",
		"Lee",
		"Johnson",
		"Chin",
		"Nguyen",
		"Farr",
		"Galigher",
		"Gold",
		"Goldman",
		"Lutess",
		"Kaltritter"
	};

	std::vector<BodyPart> bodyParts
	{
		BodyPart("Head", 100),
		BodyPart("Left Arm", 100),
		BodyPart("Right Arm", 100),
		BodyPart("Left Leg", 100),
		BodyPart("Right Leg", 100),
		BodyPart("Torso", 100)
	};

	std::vector<Trait> traitList
	{
		Trait{ "Lazy", "Hates work" },
		Trait{ "Hard Worker", "Will help other colonists willfully." },
		Trait{ "Alcoholic", "This colonist will consume far more alcohol than others." },
		Trait{ "Psychopath", "This colonist has no empathy for others or remorse for doing bad things" },
		Trait{ "Night Owl", "This colonist loves to be up at night" },
		Trait{ "Gourmand", "This colonists life revolves around food" },
		Trait{"Greedy", "This colonist tends to take more than they need."},
		Trait{"Jealous", "This coilonist hates it when anyone else has things they want"},
		Trait{"Pyromaniac", "This colonist loves to set fires."}
	};

	const int mCurrentYear{ 7423 };

	const int maxColonists{ 20 };

	std::vector<Colonist> mColonistRoster;

	// Using the factory
	ColonistFactory factory(firstNames, lastNames, traitList, bodyParts);

	for (int i = 0; i < maxColonists; i++) 
	{
		mColonistRoster.push_back(factory.CreateRandomColonist());
	}

	for (const auto& colonist : mColonistRoster)
	{
		std::cout << "Info:\n";
		std::cout << "   " << colonist.GetFirstName() << " " << colonist.GetLastName() << " - " << colonist.GetBiologicalAge() << " (" << colonist.GetChronologicalAge() << ") - Born " << mCurrentYear - colonist.GetChronologicalAge() << " years ago.\n";

		const auto& bodyParts = colonist.GetBodyParts();

		std::cout << '\n' << colonist.GetFirstName() << "'s Body Parts:\n";
		for (const auto& part : bodyParts)
		{
			std::cout << "  -" << part.GetName() << " (" << part.GetHitPoints() << ")\n";
		}

		std::cout << '\n' << colonist.GetFirstName() << "'s Traits:\n";
		for (const auto& trait : colonist.GetTraits())
		{
			std::cout << "  -" << trait.GetName() << " - " << trait.GetDescription() << '\n';
		}

		std::cout << '\n';
	}
}

Last edited on

coder777 (8444)

Normally a factory is used to create objects of derived classes/types according to some input.
But since the definition of that pattern is not that strict I think your version can be considered as a factory pattern.

kigar64551 (814)

Typically, a "factory" pattern would look like this:

Common interfaces:

class IFoo
{
public:
    virtual void foo(void) = 0;
    virtual ~IFoo() {}
};

class IBar
{
public:
    virtual void bar(void) = 0;
    virtual ~IBar() {}
};

class IFactory
{
public:
    virtual IFoo *createFoo(void) const = 0;
    virtual IBar *createBar(void) const = 0;
    virtual ~IFactory() {}
};

A concrete implementation:

class MyFoo : public IFoo
{
public:
    virtual void foo(void) { std::cout << "Hello, from MyFoo::foo()!" << std::endl; }
    virtual ~MyFoo() { std::cout << "MyFoo: Bye-bye!" << std::endl; }
};

class MyBar : public IBar
{
public:
    virtual void bar(void) { std::cout << "Hello, from MyBar::bar()!" << std::endl; }
    virtual ~MyBar() { std::cout << "MyBar: Bye-bye!" << std::endl; }
};

class MyFactory : public IFactory
{
public:
    virtual IFoo* createFoo(void) const { return new MyFoo(); }
    virtual IBar* createBar(void) const { return new MyBar(); }
};

Usage:

void test(const IFactory *const someFactory)
{
    IFoo *const someFoo = someFactory->createFoo();
    someFoo->foo();

    IBar *const someBar = someFactory->createBar();
    someBar->bar();

    delete someFoo;
    delete someBar;
}

int main()
{
    MyFactory theFactory;
    test(&theFactory);
}

Note how test() has/needs absolutely no knowledge about the concrete implementations!

Last edited on

longberns (143)

Typically, a factory comes in play when you have inheritance and the objects differ by just one or two properties.

Consider an example for a school with Students, Teachers, Admin then we can have something like this.

enum class UserType {
    STUDENT, 
    TEACHER,
    ADMIN
}
class User {
    private:
    std::string name;
    UserType type; 
    // other properties

    public:
      User(UserType type, const std::string &name, /*Other possible params*/);

    virtual void performAction() = 0;
}

class Student: public User{
    private: 
    // student-specific props

    public:
      Student(const std::string &name)
        : User(UserType::STUDENT, name){}

    virtual void performAction() override {/*concrete action*/}
}

class Teacher: public User{
    private: 
    // student-specific props

    public:
      Teacher(const std::string &name)
        : User(UserType::TEACHER, name){}

    virtual void performAction() override {/*concrete action*/}
}


class Admin: public User{
    private: 
    // student-specific props

    public:
      Admin(const std::string &name)
        : User(UserType::ADMIN, name){}

    virtual void performAction() override {/*concrete action*/}
}



class UserFactor {
    public:
    // can be unique_ptr or shared_ptr or raw pointer (not adviceable on modern C++ projects)
    static std::unique_ptr<User> create(UserType userType, const std::string &name){
        switch (userType) {
        case UserType::STUDENT:
            return std::make_unique<Student>(name);
        case UserType::TEACHER:
            return std::make_unique<Teacher>(name);
        case UserType::ADMIN:
             return std::make_unique<Admin>(name);
        // If tomorrow you have more user types in your system, just a case here
        default:
            return nullptr;
        }
    }
}


int main(){

// create a student
    auto student = UserFactor::create(UserType::STUDENT, "Awesome Name");
    // std::unique_ptr<Student> user = UserFactor::create(UserType::STUDENT, "Awesome Name");
    student->performAction();

    auto teacher = UserFactor::create(UserType::TEACHER, "Teacher name");
    teacher->performAction();
    return 0;
}

Last edited on

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