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// Copyright 2016 PlanBase Inc. & Glen Peterson
//
// 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 org.organicdesign.fp.collections;

import java.util.Comparator;

/**
 Implement compare() and hash() and you get a 100% compatible eq() for free.  If you don't need
 Comparator, just use {@link Equator}.

 A common mistake is to implement a ComparisonContext, Equator, or Comparator as an anonymous class
 or lambda, then be surprised when it is can't be serialized, or is deserialized as null.  These
 one-off classes are often singletons, which are easiest to serialize as enums.  If your
 implementation requires generic type parameters, look at how {@link #defCompCtx()} tricks the type
 system into using generic type parameters (correctly) with an enum.
*/
public interface ComparisonContext extends Equator, Comparator {
    /** Returns true if the first object is less than the second. */
    default boolean lt(T o1, T o2) { return compare(o1, o2) < 0; }

    /** Returns true if the first object is less than or equal to the second. */
    default boolean lte(T o1, T o2) { return compare(o1, o2) <= 0; }

    /** Returns true if the first object is greater than the second. */
    default boolean gt(T o1, T o2) { return compare(o1, o2) > 0; }

    /** Returns true if the first object is greater than or equal to the second. */
    default boolean gte(T o1, T o2) { return compare(o1, o2) >= 0; }

    @Override default boolean eq(T o1, T o2) { return compare(o1, o2) == 0; }

    // Enums are serializable and lambdas are not.  Therefore enums make better singletons.
    enum CompCtx implements ComparisonContext> {
        DEFAULT {
            @Override
            public int hash(Comparable