Polymorphism Puns

I still don't understand the difference between these 3.

From what I read, polymorphism is implemented using virtual functions in c++. Is that correct?

Closed sum types are unwieldy for this purpose, as adding a new "subclass" means updating code in multiple places.
The best 2 ways that I can think of are:

• using ExistentialQuantification
• Storing associated values and functions in a record

Which way is generally better? Is there another useful solution that I am not aware of?

I would greatly appreciate it if you would give me some ideas for a project/exercise; I have a slight grasp of inheritance and polymorphism but I learn best by working with something so, I want to make a project that incorporates a lot of inheritance and polymorphism but since I don't know much about them: I don't have any project ideas.

So i just learned inheritance and polymorphism in java and it seems like an unnecessary way to make the code more complex ; like why would a child class use methods and the constructor from a parent class in the end it’s the same output, and if not why would one override a constructor or a method and make the code less readable it just takes seconds to make new attributes for a new class. Maybe i sound stupid since im still a beginner but anyways can someone point out something im maybe sleeping on?

Although the words, are self explanatory, still I am looking for deep answer....

compile-time polymorphism = same method names except difference in parameter list. just like overload and default constructor. Correct method will be called based on matched parameters passed.

run-time polymorphism = subclasses with same exact method header as parent class

Hi. I've tried to cut out as much unnecassary code as I can. I can give the actual code upon request.

-- The Code --

I have 3 classes that are relevant to my problem. Here's psuedo code that only includes relevant class members/functions. First we have the base class.

        // -- .h -- //
// This class is treated as a pure virtual class. Only used for inheritance
UCLASS()
class MYGAME_API ABaseClass : public Actor                
{
public:
    ABaseClass();

    UFUNCTION(Server, Reliable)
    virtual void Interact(APlayerCharacter* Character);
}



        // -- .cpp -- //

ABaseClass::ABaseClass()
{
    bReplicates = true;
}


void ABaseClass::Interact_Implementation(APlayerCharacter* Character)
{
	UE_LOG(LogTemp, Warning, TEXT("Empty method stub. Should not be called."));
	return;
}

Next a subclass of the base class

        // -- .h -- //
UCLASS()
class MYGAME_API AChildClass : public ABase
{
public:
    void Interact_Implementation(APlayerCharacter* Character) override;
}



        // -- .cpp -- //
void AChildClass::Interact_Implementation(APlayerCharacter* Character)
{
    Destroy();
}

And lastly, a subclass of Character

        // -- .h -- //
UCLASS()
class MYGAME_API APlayerCharacter : public ACharacter
{
public:
    APlayerCharacter();

    UPROPERTY(Category = Character, VisibleAnywhere, BlueprintReadOnly)
    UCameraComponent* Camera;

    virtual void Tick(float DeltaTime) override;
    
    virtual void SetupPlayerInputComponent(class UInputComponent* PlayerInputComponent) override;

private:
    void Interact();
};



        // -- .cpp -- //
void APlayerCharacter::Interact()
{
    // For brevity, I execute a line. If I hit an object of type ABaseClass, I call
    HitInteractable->Interact(this);
}

I use blueprints classes of both APlayerCharacter and AChildClass in game. Neither have any properties, beyond a choice of mesh, modifed.

-- The Problem --

I have tested my system a few ways, and can say with confidence that the client side AChildClass is hit with the line trace done in APlayerCharacter->Interact(). The issue is that the server side AChildClass never executes any of it's code.

If I attempt the same structure in single player eve

Hello everyone! So I just learned the basics of inheritance and polymorphism in java and I am a bit lost in my code. When I create a manager which is from the subclass, I want my program to automatically adjust his/her Gross Salary depending on what the user inputs of his/her Degree so for instance if the user inputs BSc, MSc or PhD, the Gross Salary should be upgraded by adding 10, 20, or 35% respectively. Thanks in advance

public class RegularEmployees { //Superclass
    protected final String employeeID;
    private String employeeName;
    private double employeeGrossSalary;

    RegularEmployees(String employeeID, String employeeName, double employeeGrossSalary){
        this.employeeID = employeeID;
        this.employeeName = employeeName;
        this.employeeGrossSalary = employeeGrossSalary;
    }
    public double employeeNetSalary(){
        return this.employeeGrossSalary - (this.employeeGrossSalary * 0.1);
    }
    @Override
    public String toString(){
        return this.employeeName + "'s gross salary is " + this.employeeGrossSalary + "$ per month.";
    }
    public String getEmployeeName(){
        return this.employeeName;
    }
    public void setEmployeeName(String newName){
        newName = this.employeeName;
    }
    public double getEmployeeGrossSalary(){
       return this.employeeGrossSalary;
    }
    public void setEmployeeGrossSalary(double newSalary){
        newSalary = this.employeeGrossSalary;
    }
}

public class ManagerEmployees extends RegularEmployees { //Subclass
    String managerDegree;

    ManagerEmployees(String employeeID, String employeeName, double employeeGrossSalary, String managerDegree) {
        super(employeeID, employeeName, employeeGrossSalary);
        this.managerDegree = managerDegree;
    }
    @Override
    public String toString(){
        return this.managerDegree + this.getEmployeeName() + "'s gross salary is " + this.getEmployeeGrossSalary() + "$ per month.";
    }
}

I’m struggling with the concept? What’s a book or resource that explains it in depth?

The paper Lightweight Higher-Kinded Polymorphism from the author's website mentions an extended version, which I can't find.

If anybody has a link, I'd be grateful..

I've always had brain fog and issues with memory, so I have been decoding my DNA results to see if I can find out why and what I can do about it. Turns out my brain is less able to produce BDNF as I have a polymorphism, so I discovered Lions Mane as a natural way to counteract this. Curious to know if others are supplementing for the same reason.

What if microdosing, through slight shifts to altered states of consciousness, induces placebo-like effects in our body-mind as we read the associated changes in perception as "it works!", which helps us move in the direction of our intentions? We set intentions, right? Where do we arrive if we don't set intentions?

Here's the relevant code :-

fn handle_keys<T: State>(&mut self, _: &mut Game, ctx: &mut Context) -> Option<T> {

  if let Some(key) = ctx.key {
    if key == VirtualKeyCode::P {
      return Some(PlayState{});
    } else if key == VirtualKeyCode::Q {
        return Some(EndState{});
    }
  }

 None
}

I want to return Option of anything that implements the State trait. How do I do that? PlayState and EndState both implements the State trait but I still get the error. Currently the compiler is giving error in the line of "mismatched types: expected type T found struct PlayState".

edit: I know I can use Option<Box<dyn State>>, but that really makes for a very ugly function signature.

The researchers took two breeds of two species of house mice, musculus and domesticus, and cross-bred wild-type with classic inbred type, from the laboratory, and wild-type with wild-type.

This post is the next post on my blog, not part of my series comparing C++ to Rust, and a little less ambitious. Working with endianness on Rust made me think about the way APIs about endianness are designed, and it seemed to me a good starting point to talk about how Rust's generic programming facilities can be leveraged to make more maintainable, more efficient code:

https://www.thecodedmessage.com/posts/endian_polymorphism/

If you like it, subscribe to the RSS, and/or follow me on Twitter, handle also thecodedmessage.

May be a dumb question, but does 23andme give all of this information or do I need to use some third-party interpreter or something. From what I've heard 23andme does everything but explain genetic polymorphisms. Is this true? If so, I'm assuming some googling would be sufficient in telling me what everything means. Also, is Health + ancestor kit the only thing I need? Thanks

Django has powerful model inheritance features to help you use a single model to represent multiple kinds of data (polymorphism).

However, performance is terrible. That's why you should look at the following alternative ways:

> Clone this github project to see all the available techniques in action.

Using OneToOneField

Using explicit OneToOneFields to related models allows you to avoid LEFT JOINS when making SQL queries, which results in better performance.

The drawback is that creating instances becomes less easy because you need to first create the child class and then refer to it in the parent class.

Performance isn't that much better either.

Using a single model

By putting everything in one model, you avoid multi table joins. However, data storage becomes less efficient because you will be saving many rows with null fields.

It can also become quite hard to maintain if you need to store complex metadata for each child class.

Using contenttypes

This technique gives you immense flexibility because you can link the parent class to any kind of child object.

As a consequence, your data model becomes less intuitive when viewed from outside Django. For example, many models will use the content_object field, which is quite vague — data miners working on your database might go crazy!

Using a JSONField

A JSONField provides the same flexibility as contenttypes but with the same performance as using a single model because there aren't any JOINS to be made.

The issue with JSONField is that many straightforward tasks like saving an image must be done manually because we can no longer use a FileField for related models containing file attachments.

Forms and widgets must also be built manually because asking the user to supply us with a dict of their data is bad UX.

Using django-polymorphic

This package allows you to use concrete inheritance without the performance penalty.

It's probably the best way to go if you need a good balance between maintainability and performance.

The best thing about models inheriting from the PolymorphicModel class is that QuerySets return the child classes instead of the parent.

For example:

class Recipe(PolymorphicModel):
    name = models.CharField(max_length=100)A
    
class Pizza(Recipe):
    toppings = models.ManyToManyField(Topping)
    
class Burger(Recipe):
    extra_cheese = models.BooleanField(default=False)

Base class header file:

#pragma once

#include <string>

#include <iostream>

#include <sstream>

using namespace std;

class GameRules

{

public:

void Rules();

void Rules(string rule);



string GetRule();

void SetRule(string rule);

private:

string \_rule;

};

Base class cpp file:

#include "GameRules.h"

void GameRules::Rules()

{

}

void GameRules::Rules(string rule)

{

}

string GameRules::GetRule()

{

return \_rule;

}

void GameRules::SetRule(string rule)

{

\_rule = rule;

}

Derived class header file:

#pragma once

#include "GameRules.h"

class Rule1 :

public GameRules

{

public:

Rule1();

Rule1(string rule);

void SetRule1();

};

Derived class cpp file:

#include "Rule1.h"

Rule1::Rule1()

{

}

Rule1::Rule1(string rule) : GameRules (rule)

{

}

void Rule1::SetRule1()

{

cout << GetRule() << "This is rule 1" << endl;

}

I am having an issue on the bolded section of the derived class cpp file. It is saying no instance of constructor, I am not sure what I'm doing wrong? I've followed the lecture recording and it just isnt working for me?

Thanks in advance

Django has powerful model inheritance features to help you use a single model to represent multiple kinds of data (polymorphism).

However, performance is terrible. That's why you should look at the following alternative ways:

> Clone this github project to see all the available techniques in action.

Using OneToOneField

Using explicit OneToOneFields to related models allows you to avoid LEFT JOINS when making SQL queries, which results in better performance.

The drawback is that creating instances becomes less easy because you need to first create the child class and then refer to it in the parent class.

Performance isn't that much better either.

Using a single model

By putting everything in one model, you avoid multi table joins. However, data storage becomes less efficient because you will be saving many rows with null fields.

It can also become quite hard to maintain if you need to store complex metadata for each child class.

Using contenttypes

This technique gives you immense flexibility because you can link the parent class to any kind of child object.

As a consequence, your data model becomes less intuitive when viewed from outside Django. For example, many models will use the content_object field, which is quite vague — data miners working on your database might go crazy!

Using a JSONField

A JSONField provides the same flexibility as contenttypes but with the same performance as using a single model because there aren't any JOINS to be made.

The issue with JSONField is that many straightforward tasks like saving an image must be done manually because we can no longer use a FileField for related models containing file attachments.

Forms and widgets must also be built manually because asking the user to supply us with a dict of their data is bad UX.

Using django-polymorphic

This package allows you to use concrete inheritance without the performance penalty.

It's probably the best way to go if you need a good balance between maintainability and performance.

The best thing about models inheriting from the PolymorphicModel class is that QuerySets return the child classes instead of the parent.

For example:

class Recipe(PolymorphicModel):
    name = models.CharField(max_length=100)A
    
class Pizza(Recipe):
    toppings = models.ManyToManyField(Topping)
    
class Burger(Recipe):
    extra_cheese = models.BooleanField(default=False)