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Redberry is an open source computer algebra system designed for tensor manipulation. It implements basic computer algebra system routines as well as complex tools for real computations in physics. This is Redberry core, which contains the implementation of the basic computer algebra routines and general-purpose transformations.

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/*
 * Redberry: symbolic tensor computations.
 *
 * Copyright (c) 2010-2013:
 *   Stanislav Poslavsky   
 *   Bolotin Dmitriy       
 *
 * This file is part of Redberry.
 *
 * Redberry is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Redberry is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Redberry. If not, see .
 */
package cc.redberry.core.indexmapping;

/**
 * Internal interface representing a index mapping provider (IMP).
 *
 * IMP could be imagine as a processing element of a pipeline. Each such element takes a result (index mapping) of
 * the previous element and adds its own information to this result. One input index mapping could be "transformed" by
 * processing element (IMP) into zero, one, or several elements, which in turn, will be one-by-one processed by the next
 * IMP.
 *
 * It has two methods {@code tick()} and {@code take()}. The {@code tick()} method tells the current IMP to take one
 * index mapping from the previous IMP in the chin and load it into "register" inside. The {@code take()} method returns
 * the next resulting index mapping derived from mapping stored in the mentioned above register.
 *
 * Such pattern helps to avoid very long stacks in case of very complex expressions. The average stack depth is
 * proportional to the depth (number of nested tensors) of expression. In the naive implementation, otherwise, it
 * would have been proportional to the number of element in the expression.
 *
 * @author Dmitry Bolotin
 * @author Stanislav Poslavsky
 * @since 1.0
 */
interface IndexMappingProvider extends MappingsPort {

    boolean tick();

    public static class Util {

        public static final IndexMappingProvider EMPTY_PROVIDER = new IndexMappingProvider() {

            @Override
            public boolean tick() {
                return false;
            }

            @Override
            public IndexMappingBuffer take() {
                return null;
            }
        };

        public static IndexMappingProvider singleton(final IndexMappingBuffer buffer) {
            return new IndexMappingProvider() {

                IndexMappingBuffer buf = buffer;

                @Override
                public boolean tick() {
                    return false;
                }

                @Override
                public IndexMappingBuffer take() {
                    IndexMappingBuffer tmp = buf;
                    buf = null;
                    return tmp;
                }
            };
        }
    }
}