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/*
* Copyright (C) 2007 The Guava 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 com.google.common.base;
import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* Legacy version of {@link java.util.function.Function java.util.function.Function}.
*
* <p>The {@link Functions} class provides common functions and related utilities.
*
* <p>As this interface extends {@code java.util.function.Function}, an instance of this type can be
* used as a {@code java.util.function.Function} directly. To use a {@code
* java.util.function.Function} in a context where a {@code com.google.common.base.Function} is
* needed, use {@code function::apply}.
*
* <p>This interface is now a legacy type. Use {@code java.util.function.Function} (or the
* appropriate primitive specialization such as {@code ToIntFunction}) instead whenever possible.
* Otherwise, at least reduce <i>explicit</i> dependencies on this type by using lambda expressions
* or method references instead of classes, leaving your code easier to migrate in the future.
*
* <p>See the Guava User Guide article on <a
* href="https://github.com/google/guava/wiki/FunctionalExplained">the use of {@code Function}</a>.
*
* @author Kevin Bourrillion
* @since 2.0
*/
@GwtCompatible
@FunctionalInterface
@ElementTypesAreNonnullByDefault
public interface Function<F extends @Nullable Object, T extends @Nullable Object>
extends java.util.function.Function<F, T> {
@Override
@CanIgnoreReturnValue // TODO(kevinb): remove this
@ParametricNullness
T apply(@ParametricNullness F input);
/**
* <i>May</i> return {@code true} if {@code object} is a {@code Function} that behaves identically
* to this function.
*
* <p><b>Warning: do not depend</b> on the behavior of this method.
*
* <p>Historically, {@code Function} instances in this library have implemented this method to
* recognize certain cases where distinct {@code Function} instances would in fact behave
* identically. However, as code migrates to {@code java.util.function}, that behavior will
* disappear. It is best not to depend on it.
*/
@Override
boolean equals(@CheckForNull Object object);
}
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