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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to you 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 com.hazelcast.org.apache.calcite.linq4j.function;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Annotation that supplies metadata about a function parameter.
 *
 * 

A typical use is to derive names for the parameters of user-defined * functions. * *

Here is an example: * *

 * public static class MyLeftFunction {
 *   public String eval(
 *       @Parameter(name = "s") String s,
 *       @Parameter(name = "n", optional = true) Integer n) {
 *     return s.substring(0, n == null ? 1 : n);
 *   }
 * }
* *

The first parameter is named "s" and is mandatory, * and the second parameter is named "n" and is optional. * *

If this annotation is present, it supersedes information that might be * available via * {@code Executable.getParameters()} (JDK 1.8 and above). * *

If the annotation is not specified, parameters will be named "arg0", * "arg1" et cetera, and will be mandatory. */ @Retention(RetentionPolicy.RUNTIME) @Target({ElementType.PARAMETER }) public @interface Parameter { /** The name of the parameter. * *

The name is used when the function is called * with parameter assignment, for example {@code foo(x => 1, y => 'a')}. */ String name(); /** Returns whether the parameter is optional. * *

An optional parameter does not need to be specified when you call the * function. * *

If you call a function using positional parameter syntax, you can omit * optional parameters on the trailing edge. For example, if you have a * function * {@code baz(int a, int b optional, int c, int d optional, int e optional)} * then you can call {@code baz(a, b, c, d, e)} * or {@code baz(a, b, c, d)} * or {@code baz(a, b, c)} * but not {@code baz(a, b)} because {@code c} is not optional. * *

If you call a function using parameter name assignment syntax, you can * omit any parameter that has a default value. For example, you can call * {@code baz(a => 1, e => 5, c => 3)}, omitting optional parameters {@code b} * and {@code d}. * *

Currently, the default value used when a parameter is not specified * is NULL, and therefore optional parameters must be nullable. */ boolean optional() default false; }





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