/*
 * 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 org.checkerframework.checker.nullness.qual.Nullable;

Legacy version of java.util.function.Function. 
The Functions class provides common functions and related utilities. 
As this interface extends java.util.function.Function, an instance of this type can be used as a java.util.function.Function directly. To use a 
java.util.function.Function in a context where a com.google.common.base.Function is needed, use function::apply. 
This interface is now a legacy type. Use java.util.function.Function (or the appropriate primitive specialization such as ToIntFunction) instead whenever possible. Otherwise, at least reduce explicit dependencies on this type by using lambda expressions
or method references instead of classes, leaving your code easier to migrate in the future.
See the Guava User Guide article on the use of Function.
Author:
Kevin Bourrillion
Since:
2.0/**
 * 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
public interface Function<F, T> extends java.util.function.Function<F, T> {
  @Override
  @CanIgnoreReturnValue // TODO(kevinb): remove this
  @Nullable
  T apply(@Nullable F input);

  
May return true if object is a Function that behaves identically to this function. 
Warning: do not depend on the behavior of this method.
Historically, Function instances in this library have implemented this method to recognize certain cases where distinct Function instances would in fact behave identically. However, as code migrates to java.util.function, that behavior will disappear. It is best not to depend on it. /**
   * <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(@Nullable Object object);
}