By catch on
Change record status: 
Published (View all published change records)
Project: 
Drupal core
Introduced in branch: 
8.6.x
Issue links: 
https://www.drupal.org/node/1596472
Description: 

\Drupal\Core\Cache\MemoryCache\MemoryCacheInterface and \Drupal\Core\Cache\MemoryCache\MemoryCache have been added to allow classes that would previously maintain state on a protected property (as a static cache to avoid persistent cache or database lookups) to inject a service to hold that state instead.

The entity.memory_cache has been added, and is now used by all entity storage extending from \Drupal\Core\Entity\EntityStorageBase.

Custom entity storage classes that override __construct() and createInstance() should update to inject the entity.memory_cache service.