Unreal Engine 5 – Gameplay Ability System

Before we get started with setting up, I do have to mention something about it.
Implementing GAS takes some effort. It requires hundreds of lines of code, and if you’re doing a multiplayer project, prepare for some extra work.
There is no way to set up GAS in blueprints at the time of writing, unless you buy a third party plugin.
C++ is required to set up GAS.

Where do we start?

In the Unreal Engine editor, you have to enable the ‘Gameplay Abilities’ plugin, if you don’t it doesn’t matter how many lines of code you write, GAS just won’t work.

In the YourProject.build.cs file, you will have to add GameplayAbilities, GameplayTasks and GameplayTags to PublicDependencyModuleNames or PrivateDependencyModuleNames.
It doesn’t really matter if you add them in the Public or Private dependency module names

The Ability System Component:

In either your player character or playerstate C++ class, you have to include ‘AbilitySystemInterface.h’.
Do you want to keep your Ability System relevant and persistent while travelling through levels using seamless travel? Then add the Ability System to your playerstate.

Once you have added the AbilitySystemInterface header file to your includes, you can let your chosen class implement IAbilitySystemInterface.
Example:

class ACustomPlayerState : public APlayerState, public IAbilitySystemInterface

Furthermore, you have to add the Ability System Component.

UPROPERTY()
TObjectPtr<UAbilitySystemComponent> AbilitySystemComponent;

virtual UAbilitySystemComponent* GetAbilitySystemComponent() const override
{
    return AbilitySystemComponent;
}

Why a ‘TObjectPtr<>’, well because those are Unreal Engine’s replacement of raw pointers. They offer better stability in the editor, and they are likely to become the standard for Unreal Engine C++ projects.

In the constructor of the class:

AbilitySystemComponent = CreateDefaultSubobject<UAbilitySystemComponent>("AbilitySystemComponent");

In either BeginPlay or PossessedBy

AbilitySystemComponent->InitAbilityActorInfo(this, this);

That’s pretty much the basic setup for the Ability System Component.
This can be more complex, for example by granting attributes or abilities whenever ‘InitAbilityActorInfo’ happens. However, that’s not a requirement and GAS will work just fine.

The Attribute Set:

Create a new custom C++ class that will store your attributes.
For example: ACustomAttributeSet.h/.cpp.

In the header file, include ‘AttributeSet.h’ and ‘AbilitySystemComponent.h’ 
To make your life easier, there are helper macros that will automatically generate Getter and Setter functions for the attributes that will be defined later.

In order to implement those macros, add the following to the top of your Attribute Set header file:
#define CUSTOMPROJECT_ATTRIBUTE_ACCESSORS(ClassName, PropertyName) \

        GAMEPLAYATTRIBUTE_PROPERTY_GETTER(ClassName, PropertyName) \
        GAMEPLAYATTRIBUTE_VALUE_GETTER(PropertyName) \
        GAMEPLAYATTRIBUTE_VALUE_SETTER(PropertyName) \
        GAMEPLAYATTRIBUTE_VALUE_INITTER(PropertyName)

The same way as the Ability System Component, add the Attribute Set to the constructor of either your player character or playerstate.

AttributeSet = CreateDefaultSubobject<UCustomAttributeSet>("AttributeSet");

Once that is set up, you can create your very first attribute like this:

UPROPERTY()
    FGameplayAttributeData Health;
    CUSTOMPROJECT_ATTRIBUTE_ACCESSORS(UCustomAttributeSet, Health);

Be aware that attributes will always be float values.
At the moment, there’s no way to make them integer values, so if you desire an integer value, make sure that the values never becomes something with a decimal.

There’s also something called ‘meta’ attributes.
These attributes are a temporary value meant to interact with other attributes.
The most common meta attribute is ‘damage’. Since damage will interact with attributes like health and armor.