src/main/java/io/reactivex/plugins/RxJavaPlugins.java
@SuppressWarnings({ "rawtypes", "unchecked" })
    @NonNull
    public static <T> SingleObserver<? super T> onSubscribe(@NonNull Single<T> source, @NonNull SingleObserver<? super T> observer) {
        BiFunction<? super Single, ? super SingleObserver, ? extends SingleObserver> f = onSingleSubscribe;
        if (f != null) {
            return apply(f, source, observer);
        }
        return observer;
    }
@SuppressWarnings({ "rawtypes", "unchecked" })
    @NonNull
    public static <T> SingleObserver<? super T> onSubscribe(@NonNull Single<T> source, @NonNull SingleObserver<? super T> observer) {
        BiFunction<? super Single, ? super SingleObserver, ? extends SingleObserver> f = onSingleSubscribe;
        if (f != null) {
            return apply(f, source, observer);
        }
        return observer;
    }
@ SuppressWarnings ( { "rawtypes" , "unchecked" } ) @ NonNull public static < T > SingleObserver < ? super T > onSubscribe ( @ NonNull Single < T > source , @ NonNull SingleObserver < ? super T > observer ) { BiFunction < ? super Single , ? super SingleObserver , ? extends SingleObserver > f = onSingleSubscribe ; if ( f != null ) { return apply ( f , source , observer ) ; } return observer ; }
Calls the associated hook function.
@param <T> the value type
@param source the hook's input value
@param observer the observer
@return the value returned by the hook
Calls the associated hook function .