content: /*
   * 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 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.
   *
   * <p>A typical use is to derive names for the parameters of user-defined
   * functions.
   *
   * <p>Here is an example:
   *
   * <blockquote><pre>
   * public static class MyLeftFunction {
   *   public String eval(
   *       &#64;Parameter(name = "s") String s,
   *       &#64;Parameter(name = "n", optional = true) Integer n) {
   *     return s.substring(0, n == null ? 1 : n);
   *   }
   * }</pre></blockquote>
   *
   * <p>The first parameter is named "s" and is mandatory,
   * and the second parameter is named "n" and is optional.
   *
   * <p>If this annotation is present, it supersedes information that might be
   * available via
   * {@code Executable.getParameters()} (JDK 1.8 and above).
   *
   * <p>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.
     *
     * <p>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.
     *
     * <p>An optional parameter does not need to be specified when you call the
     * function.
     *
     * <p>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.
     *
     * <p>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}.
     *
     * <p>Currently, the default value used when a parameter is not specified
     * is NULL, and therefore optional parameters must be nullable.
     */
    boolean optional() default false;
  }
  