# Singletons {% hint style="success" %} verified: 2025-11-20 version: v39 {% endhint %} A singleton is a server-authoritative `MorpheusActor` which is spawned exactly once, when the server starts up. A singleton can [replicate](https://docs.msquared.io/creation/unreal-development/getting-started/networking/replicated-properties) data to game clients, and game clients can send data to the server with server [RPCs](https://docs.msquared.io/creation/unreal-development/getting-started/networking/morpheus-rpcs). Singletons are useful for the common case where you want to put a single easily-accessed object in charge of some behaviour. If no replication is required, you could handle this with server-only logic on a subsystem. However, if you want to communicate between the client and server, you need a `MorpheusActor`, so you need to use a singleton. ## How are they set up? To make a singleton, create a new blueprint class from a `MorpheusActor`. In the World Settings panel, locate the `Singletons` section, and add your new class to the `Additional Singletons` array.

If you want this singleton behaviour but for non-Morpheus Actors, use the `Non Morpheus Singletons` array. Disconnected instances of your class will be spawned on the server and all clients. (This is similar to a subsystem, but preferable if you want control over which levels the object is present in.)

{% hint style="warning" %} Singletons do not spawn automatically during automated tests. Manually spawn the required Singletons when creating automated tests that rely on them. {% endhint %} ## How to access your singleton * The easiest way to get your singleton actor is using the `GetActorOfClass` method. * This will fail (return null) if called before the singleton has been spawned. * To defer until your singleton is available, you can use the bootflow subsystem's function `HandleCommonActorsSpawned` in your actor's `BeginPlay`/`MorpheusBeginPlay`:

This example will cache the singleton of type `BPM_VendingMachineManager` once it has been spawned. Other bootflow steps after `HandleCommonActorsSpawned` would also work here, e.g. `HandleBootflowFinished`.

* Alternatively, you can use the global function `GetSingletonOnceAvailable`, specifying the `SingletonClass`. * The result will be a base `Actor`, so you will need to cast to the class you need.