e.g. Google pass in the context to every getInstance() call here https://github.com/googlesamples/android-architecture-components/blob/master/BasicRxJavaSampleKotlin/app/src/main/java/com/example/android/observability/persistence/UsersDatabase.kt

Bad, very bad code

The google code is? Why?

No matter whose. Theoretically, good version of this code is creating DB instance and passing it to constructors of components. It is not possible due to Android design flaws — okay, let's initialize it in

Application

using

lazy

. Hand-written double-checks should be avoided.

@Volatile

is excessive here.

Here's something to never mess your codebase like this because of application context requirement: https://github.com/LouisCAD/Splitties/blob/master/appctx/README.md

@miha-x64 do you mean not using a singleton, and instead passing an instance to whatever component needs it? i believe the double check is for double checked lockin

@luke_c I mean that we sometimes must use singletons only due to Android design flaws. Double check is 100% for double checked locking, but it's written incorrectly;

lazy

should be used instead.