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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  package org.apache.commons.lang3.function;
19  
20  import java.util.function.Supplier;
21  
22  /**
23   * A functional interface like {@link Supplier} that declares a {@link Throwable}.
24   *
25   * @param <T> Return type.
26   * @param <E> The kind of thrown exception or error.
27   * @since 3.11
28   */
29  @FunctionalInterface
30  public interface FailableSupplier<T, E extends Throwable> {
31  
32      /**
33       * Returns the singleton supplier that always returns null.
34       * <p>
35       * This supplier never throws an exception.
36       * </p>
37       *
38       * @since 3.14.0
39       */
40      @SuppressWarnings("rawtypes")
41      FailableSupplier NUL = () -> null;
42  
43      /**
44       * Returns the singleton supplier that always returns null.
45       * <p>
46       * This supplier never throws an exception.
47       * </p>
48       *
49       * @param <T> Supplied type.
50       * @param <E> The kind of thrown exception or error.
51       * @return The NUL singleton.
52       * @since 3.14.0
53       */
54      @SuppressWarnings("unchecked")
55      static <T, E extends Exception> FailableSupplier<T, E> nul() {
56          return NUL;
57      }
58  
59      /**
60       * Supplies an object
61       *
62       * @return a result
63       * @throws E if the supplier fails
64       */
65      T get() throws E;
66  }