How is the CompositionLocal structure implemented and functioning within the system?

CompositionLocal in Android (more often in Jetpack Compose) is a mechanism for passing data down the component tree without the need to explicitly pass them through parameters. It is similar to context in React.

The implementation is based on storing a value in a special object that can have a default value and be overridden in the local composition context. When a child element requests the value of CompositionLocal, it receives the current value from the nearest ancestor that has overridden it, or the default value.

Thus, CompositionLocal allows convenient sharing of state or configuration between components without cluttering function signatures with parameters.

Example of usage:

val LocalUser = compositionLocalOf { "Guest" }

@Composable
fun Greeting() {
    val user = LocalUser.current
    Text("Hello, $user!")
}

@Composable
fun App() {
    CompositionLocalProvider(LocalUser provides "Alice") {
        Greeting() // will output: Hello, Alice!
    }
}