content: /*
   * Copyright (C) 2020 ActiveJ LLC.
   *
   * 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.activej.inject.annotation;
  
  import io.activej.inject.Key;
  import io.activej.inject.Qualifiers;
  
  import java.lang.annotation.Retention;
  import java.lang.annotation.Target;
  
  import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
  import static java.lang.annotation.RetentionPolicy.RUNTIME;
  
  /**
   * This is a marker meta-annotation that declares an annotation as the one that
   * can be used as a {@link Key key} qualifier.
   * <p>
   * Creating a custom stateless qualifier annotation is as easy as creating your own annotation with no parameters
   * and annotating it with {@link QualifierAnnotation}. That way, an actual class of your stateless qualifier annotation
   * will be used as a qualifier.
   * <p>
   * If you want to create a stateful annotation, you should also annotate it with {@link QualifierAnnotation}.
   * Additionally, you need to get an instance of it with compatible equals method (you can use {@link Qualifiers}.NamedImpl class as an example)
   * After that, you can use your annotation in our DSL and then make keys programmatically with created qualifier instances.
   */
  @Target(ANNOTATION_TYPE)
  @Retention(RUNTIME)
  public @interface QualifierAnnotation {
  }
  