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Components

Once you’ve worked out what entities your world will have, the next step is to work out what the components of the entities should be.

For best practices when using components, see the Component best practices page.

Elements of components

Components can have three elements:

properties describe persistent values that change over time
events describe transient things that have happened to an entity
commands describe things that other entities can ask this entity to do

Each component can have many properties, events and commands. For example, an explosive barrel might have the following components:

Component	Name	Type
Position	Coordinates	Property: coordinates
FuelContainer	FuelType	Property: enum
	Capacity	Property: float
	CurrentAmount	Property: float
Explosive	Explode	Command
	ExplosiveRange	Property: float
	HasExploded	Property: boolean
Damageable	CurrentDamage	Property: float
Damageable	MaxDamage	Property: float
Flammable	OnFire	Property: boolean
Flammable	CatchFire	Event

It’s important that everything that you need to define your entity is stored in components. SpatialOS is a distributed system, running over many machines which may fail at any time, so your entity must be able to be recreated from the components.

Any local state stored on a worker can be easily lost.

Writing components

Write up your components in the schema, using the SpatialOS schemalang. This schema is used to generate code that all workers can use to read and manipulate components.

For full details, see the schema documentation.

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