code: /*
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.rxjava3.internal.operators.observable;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.functions.Supplier;
  import io.reactivex.rxjava3.internal.observers.DeferredScalarDisposable;
  import io.reactivex.rxjava3.internal.util.ExceptionHelper;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  /**
   * Calls a Supplier and emits its resulting single value or signals its exception.
   * @param <T> the value type
   * @since 3.0.0
   */
  public final class ObservableFromSupplier<T> extends Observable<T> implements Supplier<T> {
  
      final Supplier<? extends T> supplier;
  
      public ObservableFromSupplier(Supplier<? extends T> supplier) {
          this.supplier = supplier;
      }
  
      @Override
      public void subscribeActual(Observer<? super T> observer) {
          DeferredScalarDisposable<T> d = new DeferredScalarDisposable<>(observer);
          observer.onSubscribe(d);
          if (d.isDisposed()) {
              return;
          }
          T value;
          try {
              value = ExceptionHelper.nullCheck(supplier.get(), "Supplier returned a null value.");
          } catch (Throwable e) {
              Exceptions.throwIfFatal(e);
              if (!d.isDisposed()) {
                  observer.onError(e);
              } else {
                  RxJavaPlugins.onError(e);
              }
              return;
          }
          d.complete(value);
      }
  
      @Override
      public T get() throws Throwable {
          return ExceptionHelper.nullCheck(supplier.get(), "The supplier returned a null value.");
      }
  }
  