UEFN Verse: Class Specifiers

Class specifiers are used when creating classes to define behaviors and characteristics. This article will present the main ones.

The <abstract> specifier is used to create superclasses with common fields and methods to be inherited by subclasses.

An abstract class allows the declaration of methods without a body (it has no code) that must be overridden in a subclass.

The code below creates the abstract class base_bonus. The ApplyBonus() method has no body.

base_bonus := class<abstract>():
    BonusId : int
    Name : string 
    BonusValue: int
	
    BonusData(): string =
        "BonusId: {BonusId} | Name: {Name} | BonusValue: {BonusValue}"

    ApplyBonus() : void

It is not possible to create instances of an abstract class. The code below generates a compilation error.

BaseBonus : base_bonus = base_bonus{BonusValue := 20,  Name := "Generic"}

The <concrete> specifier indicates that all fields of the class must have default values, allowing the creation of instances with an empty archetype.

The code below creates the concrete class score_bonus using base_bonus as the superclass. All fields have been given default values ​​and the ApplyBonus() method has been overridden.

score_bonus := class<concrete>(base_bonus):
    BonusId<override> : int = 2
    Name<override> : string = "Score MEDIUM"
    BonusValue<override>: int = 50
	
    ApplyBonus<override>() : void =
        Print("Adding {BonusValue} to SCORE.")

This code creates an instance of score_bonus using an empty archetype {}.

ScoreBonusDefault : score_bonus = score_bonus{}

The <final> specifier is used to indicate that a class cannot have subclasses. This specifier can also be used on fields and methods to indicate that they cannot be overridden.

The code below creates the final class time_bonus using base_bonus as the superclass.

time_bonus := class<final>(base_bonus):
    BonusId<override> : int = 1
	
    ApplyBonus<override>() : void =
        Print("Adding {BonusValue} to TIME.")

The new time_bonus class cannot be used as a superclass. The following code generates a compilation error.

time_bonus_variation := class(time_bonus):

Let's combine these examples into a single file so we can test it on UEFN. I created a verse device called class_specifiers_device and used this code:

using { /Fortnite.com/Devices }
using { /Verse.org/Simulation }
using { /UnrealEngine.com/Temporary/Diagnostics }

base_bonus := class<abstract>():
    BonusId : int
    Name : string 
    BonusValue: int
	
    BonusData(): string =
        "BonusId: {BonusId} | Name: {Name} | BonusValue: {BonusValue}"

    ApplyBonus() : void

time_bonus := class<final>(base_bonus):
    BonusId<override> : int = 1
	
    ApplyBonus<override>() : void =
        Print("Adding {BonusValue} to TIME.")

score_bonus := class<concrete>(base_bonus):
    BonusId<override> : int = 2
    Name<override> : string = "Score MEDIUM"
    BonusValue<override>: int = 50
	
    ApplyBonus<override>() : void =
        Print("Adding {BonusValue} to SCORE.")		

class_specifiers_device := class(creative_device):

    TimeBonus : time_bonus = time_bonus{BonusValue := 30, Name := "Time MEDIUM"}

    ScoreBonusDefault : score_bonus = score_bonus{}

    OnBegin<override>()<suspends>:void= 

        Print( ScoreBonusDefault.BonusData() )
        ScoreBonusDefault.ApplyBonus()

This Verse device simply executes the two methods of the ScoreBonusDefault instance to write some messages to the log. The device was created to illustrate the use of class specifiers. 

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