SystemEntity and EntityManager

[MathiasPaulin]

As mentioned in the PR #763 and the issue #767, The singleton SystemEntity is managed by the EntityManager and the lifetime of this singleton is the one of the EntityManager.
The EntityManager, that is not a singleton, has the lifetime of the Engine and is fully managed by the Engine

This lifetime restriction make the notion of singleton quite unappropriated for SystemEntity.
Note that this discussion should also be related to other singleton whose lifetime is the one of the Engine :

• ComponentMessenger
• DebugRender
• SystemEntity

As all of these singletons are specific to the Engine instance (that is a singleton), we can change their status to private attribute of the engine, with methods in the Engine allowing to access these attributes. We already did this for SignalManager, RenderObjectManager, ShaderManager and TextureManager.

ComponentMessenger, DebugRender and SystemEntity, whose lifetime is the one of the Engine should be integrated into the Engine as the other managers.

If we do this, there will remain only 2 singletons in the Radium libs :

• the Engine (in the Radium::Engine library component)
• the KeyMappingManager (in the Radium::Gui library component)

So the question is :

• if some objects have the lifetime of another object and should be used only within the constext defined by this other object, could they be singletons ?

I think they don't and propose to integrate the 3 singletons above as private attributes into the Engine.

What about this proposal ?

[nmellado]

I am fine with removing the singletons and make them as private attribute of Engine.
We just need to be sure that if someone runs two Engines in the same app (I don't know why, but anyway), these attributes also work properly (ie. no static data structures).

[MathiasPaulin]

Engine is a singleton, so, there is no way to run two Engines in the same app, right ?