qgis - Is QgsMapLayerRegistry removed in QGIS3?

Is QgsMapLayerRegistry going to be availabe in pyqgis with QGIS3

When I typed it into the QGIS python console (2.99), python seems to recognize it because it auto-completes qgis.core.QgsMapLayerRegistry, but then gives an error that it's not there:

Traceback (most recent call last):
  File "/usr/lib/python3.5/code.py", line 91, in runcode
    exec(code, self.locals)
  File "", line 1, in 
AttributeError: module 'qgis.core' has no attribute 'QgsMapLayerRegistry'

I tried this with two versions of QGIS 2.99 (one in 01/07 and on in 06/17). Both versions give the same error. import doesn't work either:

>>>from qgis.core import QgsMapLayerRegistry
Traceback (most recent call last):
  File "/usr/lib/python3.5/code.py", line 91, in runcode

    exec(code, self.locals)
  File "", line 1, in 
ImportError: cannot import name 'QgsMapLayerRegistry'

Is QgsMapLayerRegistry removed in QGIS3?

Answer

Yes it has been removed, but alternatives exist.

Changes of the 3.0 API are listed here:

https://qgis.org/api/api_break.html

QgsMapLayerRegistry: Its functionality has been moved to QgsProject.

The main reason is, that QgsMapLayerRegistry is/was a singleton and therefore only a single registry could ever exist. With this constraint removed, major roadblocks are out of the way to implement new things like having multiple projects open side-by-side.