/*
 * Copyright (C) 2010 Google Inc.
 *
 * 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 com.google.inject.spi;

import com.google.inject.Binding;
import com.google.inject.Provider;

A Provider that is part of an extension which supports a custom BindingTargetVisitor.
When an extension binds a provider instance, the provider can implement this interface to allow users using the Binding.acceptTargetVisitor(BindingTargetVisitor) method to visit a custom visitor designed for that extension. A typical implementation within the extension would look like 
<V, B> V acceptExtensionVisitor(BindingTargetVisitor<B, V> visitor, ProviderInstanceBinding<? extends B> binding) {
  if(visitor instanceof MyCustomExtensionVisitor) {
    return ((MyCustomExtensionVisitor<B, V>)visitor).visitCustomExtension(customProperties, binding);
  } else {
    return visitor.visit(binding);
  }
}
'MyCustomExtensionVisitor' in the example above would be an interface the extension provides that
users can implement in order to be notified of custom extension information. These visitor
interfaces must extend from BindingTargetVisitor.
Author:
sameb@google.com (Sam Berlin)
Since:
3.0/**
 * A Provider that is part of an extension which supports a custom BindingTargetVisitor.
 *
 * <p>When an extension binds a provider instance, the provider can implement this interface to
 * allow users using the {@link Binding#acceptTargetVisitor(BindingTargetVisitor)} method to visit a
 * custom visitor designed for that extension. A typical implementation within the extension would
 * look like
 *
 * <pre>
 * &lt;V, B> V acceptExtensionVisitor(BindingTargetVisitor&lt;B, V> visitor, ProviderInstanceBinding&lt;? extends B> binding) {
 *   if(visitor instanceof MyCustomExtensionVisitor) {
 *     return ((MyCustomExtensionVisitor&lt;B, V>)visitor).visitCustomExtension(customProperties, binding);
 *   } else {
 *     return visitor.visit(binding);
 *   }
 * }</pre>
 *
 * 'MyCustomExtensionVisitor' in the example above would be an interface the extension provides that
 * users can implement in order to be notified of custom extension information. These visitor
 * interfaces must extend from BindingTargetVisitor.
 *
 * @since 3.0
 * @author sameb@google.com (Sam Berlin)
 */
public interface ProviderWithExtensionVisitor<T> extends Provider<T> {

  
Instructs the extension determine if the visitor is an instance of a custom extension visitor,
and if so, visit it using that method. If the visitor is not an instance of the custom
extension visitor, this method MUST call visitor.visit(binding).
Due to issues with generics, the type parameters of this method do not relate to the type of
the provider. In practice, the 'B' type will always be a supertype of 'T'.
/**
   * Instructs the extension determine if the visitor is an instance of a custom extension visitor,
   * and if so, visit it using that method. If the visitor is not an instance of the custom
   * extension visitor, this method <b>MUST</b> call visitor.visit(binding).
   *
   * <p>Due to issues with generics, the type parameters of this method do not relate to the type of
   * the provider. In practice, the 'B' type will always be a supertype of 'T'.
   */
  <B, V> V acceptExtensionVisitor(
      BindingTargetVisitor<B, V> visitor, ProviderInstanceBinding<? extends B> binding);
}