Singletons

Singletons, full type being /datum/singleton, are a class of lazy-initialized global singletons for holding shared information and state. They are unique by type.

Let's unpack a little:

• Lazy-initialized: a singleton of a given type does not exist until it has first been queried. After that, it will remain alive in the game world.
• Global singleton: a single instance of every singleton subtype should exist at any one time. This instance is shared between all users.
• Unique by type: the "name" of a singleton is its full type. As mentioned before, no more than one instance of any singleton type should exist.

Basic Usage

Behind the scenes, singletons are simple datums with a special interaction via the Singletons repository, accessed through the GET_SINGLETON() defines. So you can simply create them as you would create a unique datum class:

/singleton/my_singleton
	var/a = 4

As said, this class gets created once we first query for it. To do so, we simply use the GET_SINGLETON(singleton) define:

/proc/main()
	var/singleton/my_singleton/s = GET_SINGLETON(/singleton/my_singleton)
	world << s.a // will print "4"

Variations

The Singletons contains functions to get multiple singleton, or all types of a specific singleton, or all subtypes. See the following defines:

• GET_SINGLETON_TYPE_MAP(singleton)
• GET_SINGLETON_SUBTYPE_MAP(singleton)
• GET_SINGLETON_TYPE_LIST(singleton)
• GET_SINGLETON_SUBTYPE_LIST(singleton)