Abstract Classes

Here is a basic example of abstract and derived classes

public abstract class BaseClass : UdonSharpBehaviour
{
	// Abstract classes can include variables, properties and methods
    // Using the abstract keyword on any of the previously mentioned will require the implementation in the derived class
	public abstract bool RequiredProperty { get; set; }

	public abstract void RequiredAbstractMethod(); // Abstract methods can't have body, their behaviour must be implemented in the derived class
    
    // The "virtual" keyword allows us to define the "default" behaviour of a method, which can be overriden in the derived class
    public virtual void VirtualMethod()
    {
    	RequiredAbstractMethod();
        RequiredProperty = true;
    }
}

public class DerivedClass : BaseClass
{
	// Properties can be implemented as we wish, getters and setters can point to to anything
    // In this example the property just points to a private boolean in the derived class
	public override bool RequiredProperty { get => privateBoolean; set => privateBoolean = value; }
    
	private bool privateBoolean;

	// Abstract methods must be implemented in derived classes
	public override void RequiredAbstractMethod()
    {
    	// Here we add any code we want to execute that we can call with either 
    }
}

In this example we want to create an abstract Vehicle that has shared characteristics across all transportation methods via land, air and sea.

[RequireComponent(typeof(Rigidbody))] // RequireComponent attributes will be inherited by derived class
[RequireComponent(typeof(Animator))]
[RequireComponent(typeof(VRCObjectSync))]
[UdonBehaviourSyncMode(BehaviourSyncMode.Continuous)] // Sync mode will be inherited by derived classes, so you may define it in any class you want
public abstract class Vehicle : UdonSharpBehaviour
{
	// Abstract classes can have private variables that won't be accessible from derived classes
	private Rigidbody rb;
    private VRCObjectSync objectSync;
    private Animator animator;
    
    // In this example, you obviously wouldn't want any script tampering with the private variables of the abstract class, so we will add our own properties with only getter exposed
    public Rigidbody RB { get => rb; }
    public VRCObjectSync ObjectSync { get => objectSync; }
    public Animator Animator { get => animator; }
    
    // By adding the "protected" access modifier, we can make private variables, properties or methods accessible to the derived class
    private protected void InitializeAbstractVehicle()
    {
    	// Any operations shared by all derived classes can be included in the abstract class
    	rb = GetComponent<Rigidbody>();
        objectSync = GetComponent<VRCObjectSync>();
        animator = GetComponent<Animator>();
    }
    
    // By adding a "virtual" keyword we can define the "default" behaviour of a method, which can overriden in derived classes
    // In this example we want to be able to call Vehicle._RespawnVehicle() or LandVehicle._RespawnVehicle() and always call the respawn method on the object sync
    public virtual void _RespawnVehicle()
    {
    	objectSync.Respawn();
    }
}

public class LandVehicle : Vehicle
{

}

public class AirVehicle : Vehicle
{

}

public class SeaVehicle : Vehicle
{

}