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/*
* Copyright (C) 2016 The Dagger Authors.
*
* 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 dagger;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import dagger.internal.Beta;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import javax.inject.Inject;
import javax.inject.Qualifier;
/**
* Annotates methods that declare bindings for {@code Optional} containers of values from bindings
* that may or may not be present in the component.
*
* <p>If a module contains a method declaration like this:
*
* <pre>
* {@literal @BindsOptionalOf} abstract Foo optionalFoo();</pre>
*
* then any binding in the component can depend on an {@code Optional} of {@code Foo}. If there is
* no binding for {@code Foo} in the component, the {@code Optional} will be absent. If there is a
* binding for {@code Foo} in the component, the {@code Optional} will be present, and its value
* will be the value given by the binding for {@code Foo}.
*
* <p>A {@code @BindsOptionalOf} method:
*
* <ul>
* <li>must be {@code abstract}
* <li>may have a {@linkplain Qualifier qualifier} annotation
* <li>must not return {@code void}
* <li>must not have parameters
* <li>must not throw exceptions
* <li>must not return an unqualified type with an {@link Inject @Inject}-annotated constructor,
* since such a type is always present
* </ul>
*
* <p>Other bindings may inject any of:
*
* <ul>
* <li>{@code Optional<Foo>} (unless there is a {@code @Nullable} binding for {@code Foo}; see
* below)
* <li>{@code Optional<Provider<Foo>>}
* <li>{@code Optional<Lazy<Foo>>}
* <li>{@code Optional<Provider<Lazy<Foo>>>}
* </ul>
*
* <p>If there is a binding for {@code Foo}, and that binding is {@code @Nullable}, then it is a
* compile-time error to inject {@code Optional<Foo>}, because {@code Optional} cannot contain
* {@code null}. You can always inject the other forms, because {@link Provider} and {@link Lazy}
* can always return {@code null} from their {@code get()} methods.
*
* <p>Explicit bindings for any of the above will conflict with a {@code @BindsOptionalOf} binding.
*
* <p>If the binding for {@code Foo} is a {@code @Produces} binding, then another {@code @Produces}
* binding can depend on any of:
*
* <ul>
* <li>{@code Optional<Foo>}
* <!-- TODO(dpb): Update this once producers support nullability checks -->
* <li>{@code Optional<Producer<Foo>>}
* <li>{@code Optional<Produced<Foo>>}
* </ul>
*
* <p>You can inject either {@code com.google.common.base.Optional} or {@code java.util.Optional}.
*/
@Documented
@Beta
@Retention(RUNTIME)
@Target(METHOD)
public @interface BindsOptionalOf {}
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