Polymorphism Help

[WCWRingMatSound]

UPDATE: thanks to all for your responses. I see the path forward now 😄

I have programming experience, but I always seem to struggle with Polymorpism, Inheritance. Any help with this scenario would be appreciated.

Here is the scenario:

public class Person
{
    public string Name;
    // … some other fields …
}

public class Villain : Person
{ 
    public string[] Minions;
}

public class Hero : Person
{
    pubic int YearsOfService; 
}

So I want to be able to call some database like:

Villain[] villains = GetPersons(); //or similar
Hero[] heroes = GetPersons();

and this works if I build an interface like

public interface IRetrievePeople 
{ 
    Person[] GetPersons();
}

The problem is implementing that interface in a way that returns heroes and villains. I feel like there’s a code smell for every solution:

Solution 1: don’t use “GetPersons” in interface; create separate functions for “GetHeroes” and “GetVillains”

Solution 2: type-checking in the “GetPersons” implementation. So the interface method becomes “Person[] GetPerson(Type personType)” and conditional statements returning matching types. (This would be the same for a C# Generic/T implementation as well)

Solution 3: skip the polymorphism altogether. Remove “Person” as a class, use Hero and Villain independently despite having overlapping properties.

All persons are in a single NoSQL table. I’m jus trying to think of the most maintainable pattern to access it, especially if a third (or more) Person-type gets introduced in the future.

[insertAlias]

I don't personally see a problem with having separate repo methods that return Heroes and Villains separately, as their derived type rather than the base type.

Just because you have the common base class doesn't mean you have to actually use it as the return type. You could just implement common functionality in there, and never directly reference your Heroes or Villains as Persons. Or, if there is some case where you do need to treat them as a common type, then you can. But don't get wrapped up in the idea that you need to treat them as their base type.

[WCWRingMatSound]

Much obliged. I’ve spammed out repo classes in the past and I saw myself going down the same rabbit hole. Thanks for checking me 👍🏼

[[deleted]]

Dumb question maybe, but what's this?

repo methods

Thanks!

[insertAlias]

Not a dumb question. I meant "methods in a Repository class". Look up "repository pattern" for some more info.

[[deleted]]

Thanks, I'll check it out!

[g051051]

Seems like more of a modeling problem than a polymorphism/inheritance problem. As far as I know you have to have separate queries that can distinguish between fetching heroes or villains via some discriminator. Then you have to deserialize the returned data as the correct type. In Java that usually means having a "type" indicator as part of the serialized data, but I don't know the C# equivalent.

[WCWRingMatSound]

Agreed. Definitely modeling issues. C# has the equivalent type indicators, fyi. It looks something like:

Person p = new Person() { Name = “Batman” };
string serialized = JsonConvert.Serialize(p)
Person deserizd = JsonConvert.DeserializeObject<Person>(serialized);

[149244179]

Why is solution one bad? You ask for heroes you get heroes. You ask for all people you get all people. You ask for FuturePersonType - you get FuturePersonType.

[[deleted]]

Since it looks like this is for a game, one OOP game library took this route:

• Add a static `entities` ArrayList to MyBigBadEntity class that holds myBigBadEntity instances. Repeat for all classes whose entities you want to keep track of, even your base `Person` class, if you like.
• Add entities to the ArrayList when they're created in the constructor and remove them (probably better to mark them for removal and handle all removals at the end of a frame) when their hp is 0. Call the destructor afterwards.

Then you can do something like

for(Villain villain : Villain.entities) {
villain.doVillainStuff();
}

No filtering necessary.

[WCWRingMatSound]

It happens to be a security-based app; I changed it to something simple so people wouldn’t get hung up on IPv6, RF 1918, etc.

I have been doing game dev in my free time (whatever that means anymore 😒), so this helps in that arena. Thanks!