unity-atoms/docs/introduction/overview.md

---
id: overview
title: Overview and philosopy
hide_title: true
sidebar_label: Overview and philosopy
---

# Overview and philosopy

Unity Atoms is an event based system that encourages the game to be as data-driven as possible. The four most fundamental parts of Unity Atoms are:

-   Variables
-   Events
-   Listeners
-   Responses

## Variables

Variables are data / variables stored as Scriptable Objects. Because Variables are stored as Scriptable Objects they are not part of any scene, but could be instead be seen as part of a global shared game state. Variables are also designed to make it easy to inject (via the Unity Inspector) to your MonoBehaviours.

It is possible to attach an event to a Variable that gets raised when its updated. This makes it possible to write more data-driven code.

It is also possible to attach another event to a Variable that also gets raised when a Variable is changed, but that contains both the old and the new value of the Variable.

Unity Atoms also offer some variations / additions to Variables such as Contants, References and Lists.

### Constants

Exactly the same as Variables, but can not be changed via script and therefore does not contain the change events that Variables does. The idea is to use Constants for for example tags instead of hard coding tags in your scripts.

### References

References can be toggled between `use as constant` or `use variable` via the Unity Inspector. When a reference is `used as constant` then it functions exactly like a regular serialized variable in a MonoBehaviour script. However, when it is set to `use variable` it functions exactly like a Variable.

### Lists

A List is an array of values that is stored as a Scriptable Object. There is the possibility to add Events for when the following happens to the list:

-   An item is added to the List.
-   An item is removed from the List.
-   The List is cleared.

## Events

An event is a thing that happens in the game that others can listen / subscribe to. Events in Unity Atoms are also Scriptable Objects that lives outside of a specific scene. It is possible to raise an Event from the Unity Inspector for debug purposes.

## Listeners

A Listener listens / observes / subscribes to an event and raises / invokes zero to many responses to that event. Listeners are MonoBehaviours and lives in a scene. See below for more information on the type of responses there are.

## Responses

A responses is raised by a listener in response to an event. Responses can live both in the scene as [UnityEvents](https://docs.unity3d.com/ScriptReference/Events.UnityEvent.html) or outside the scene as a Scriptable Object in the shape of an Action.

### Actions

An Action in Unity Atoms is a C# function as a Scriptable Object. An Action can be used as a response in a Listener.

### Game Functions

A Function in Unity Atoms is basically the same as an Action, but while an Actions does not return something a Function does.