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.spark.sql.catalyst.expressions;
19 
20 import org.apache.spark.annotation.DeveloperApi;
21 
22 import java.lang.annotation.Retention;
23 import java.lang.annotation.RetentionPolicy;
24 
25 /**
26  * ::DeveloperApi::
27 
28  * A function description type which can be recognized by FunctionRegistry, and will be used to
29  * show the usage of the function in human language.
30  *
31  * `usage()` will be used for the function usage in brief way.
32  * `extended()` will be used for the function usage in verbose way, suppose
33  *              an example will be provided.
34  *
35  *  And we can refer the function name by `_FUNC_`, in `usage` and `extended`, as it's
36  *  registered in `FunctionRegistry`.
37  */
38 @DeveloperApi
39 @Retention(RetentionPolicy.RUNTIME)
40 public @interface ExpressionDescription {
usage()41     String usage() default "_FUNC_ is undocumented";
extended()42     String extended() default "\n    No example/argument for _FUNC_.\n";
43 }
44