How to efficiently determine all scene objects within range R of some given object X?

Question

Are there any gems in the engine API that would make it possible to efficiently ask the scene tree "find all objects X distance away from object Y". This is not as easy as "scan everything" since that is a big-oh of n-squared solution: "for each object Y in scene tree compare with every object (as X) in scene tree". BSPs aren't good since their setup is an offline algorithm (meaning BSPs can't change easily with runtime object movement). I could implement a range tree for one axis (but the storage blows up to "N to the number of dimensions" for more than one). So I'm not sure what I should use here. Assume LOTS of objects to check (large N).

Comments

Why not simply use the collision engine by calling space_state.intersect_shape()?
Or maybe, divide the world into a grid for faster queries? (but Godot already does that)
http://docs.godotengine.org/en/latest/classes/class_physics2ddirectspacestate.html?highlight=intersect_shape#physics2ddirectspacestate

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You want to check this for many objects or rather single ones like Player? If latter then you can just add area node to player and use area interface.

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basically as was discussed on FB using the collision system with spheres to represent the ranges and bounding cubes to represent objects (layered and masked so cube/sphere emit in/out signals but no cube/cube nor sphere/sphere signals). these could simply be added onto objects as children

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If I understand well, you can do it with an Area, with the signal onenter_body.