Registries are a very important concept in Terra. They allow Terra, the platform, and other addons to know your addon’s objects exist, and how to identify those objects.

What is a Registry

A registry can be thought of as a map of Registry Keys to Entries. Registries register a particular type of object, grouping them together. Registries uniquely identify their entries, only one entry can exist per key.

What are Registries Used For?

In Terra, registries are used for referencing items between addons and config packs. They provide a simple way for addons and configs to create and share data between each other with no special compatibility measures required.

Working with Registries

Most interactions with the Terra API require working with registries at some point.

Registry Keys

Registries use RegistryKeys to identify values. Registry Keys consist of a Namespace and an Identifier.

Registry keys can be created by the RegistryKey#parse method, to parse a registry key with the namespace:id syntax. They can also be created with a namespace and ID with the RegistryKey#of method.


The namespace is the provider of the value being registered, usually your addon or config pack. Objects which hold a namespace implement the Namespaced interface. Namespaced objects can create registry keys in their namespace via the key(String identifier) method.


The identifier is the name of the value itself. Multiple items with the same identifier may exist, so long as they have different namespaces. Items which provide their own identifiers implement StringIdentifiable.


The Keyed interface is implemented by objects which provide their own Registry Keys.

Getting a Registry

Registries can be retrieved from objects implementing RegistryHolder. Most commonly, this will be a ConfigPack. RegistryHolder defines several methods for fetching registries, most commonly you’ll use the methods accepting a Class instance, and Type Keys. There is an unchecked method which accepts a raw Type instance, its use is generally discouraged.

Let’s get the Structure registry from a config pack instance!

pack.getRegistry(Structure.class); // returns the unique registry holding instances of Structure.

Getting a Writable Registry

The registry we fetched in the previous example is read-only. It’s useful for retrieving information, but you’ll frequently want to register your own objects. For that, we’ll use a CheckedRegistry, which can be retrieved from a CheckedRegistryHolder in the same manner as Registry can be retrieved from RegistryHolder.

Let’s register something!

pack.getCheckedRegistry(Structure.class).register(myAddon.key("my_structure"), new MyStructure()); // Register a new instance of MyStructure, with a Registry Key "my_addon:my_structure"

Creating a Registry

Sometimes, you may wish to create a registry for registering your own objects. Objects which implement RegistryProvider can create CheckedRegistry instances via their #getOrCreateRegistry methods.