CompletableOperator

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
```
@FunctionalInterface
public interface CompletableOperator
```
Interface to map/wrap a downstream observer to an upstream observer.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`@NonNull CompletableObserver`	`apply(@NonNull CompletableObserver observer)`	Applies a function to the child `CompletableObserver` and returns a new parent `CompletableObserver`.

- Method Detail
  - apply
```
@NonNull
@NonNull CompletableObserver apply(@NonNull
                                   @NonNull CompletableObserver observer)
                            throws java.lang.Throwable
```
    Applies a function to the child CompletableObserver and returns a new parent CompletableObserver.
    
    Parameters:
    
    observer - the child CompletableObserver instance
    
    Returns:
    
    the parent CompletableObserver instance
    
    Throws:
    
    java.lang.Throwable - on failure