I'm considering switching from Firebase DB to Realm.io.
For my app, I need sharing items between users (in a many-to-many fashion).
In Firebase there is a permissions language (and the Bolt compiler).
What is the equivalent model in Realm.io?
Can I share objects between users, with controlled permissions?
EDIT: I'm talking about fine-grained per-object sharing, not coarse-grained per-database sharing.
In the current release, permissions are defined per Realm (collection of objects), not fine-grained per object. You can obviously easily implement a "filtering" functionality unless you have strict security requirements that prohibit having some "irrelevant" data physically on a device despite it being fully encrypted.
If there are specific details you don't find sufficiently covered in the official docs please elaborate what those are.