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Standard ML interpreter, with relational extensions, implemented in Java
There is a newer version: 0.7.0
/*
 * Licensed to Julian Hyde under one or more contributor license
 * agreements.  See the NOTICE file distributed with this work
 * for additional information regarding copyright ownership.
 * Julian Hyde licenses this file to you 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 net.hydromatic.morel.util;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Map;

import static com.google.common.base.Preconditions.checkArgument;

/** Immutable list of pairs.
 *
 * @param  First type
 * @param  Second type
 */
public interface ImmutablePairList extends PairList {

  /** Creates an empty ImmutablePairList. */
  @SuppressWarnings("unchecked")
  static  ImmutablePairList of() {
    return (ImmutablePairList) PairLists.EMPTY;
  }

  /** Creates a singleton ImmutablePairList. */
  static  ImmutablePairList of(T t, U u) {
    return new PairLists.SingletonImmutablePairList<>(t, u);
  }

  /** Creates an ImmutablePairList with one or more entries. */
  static  PairList copyOf(T t, U u, Object... rest) {
    checkArgument(rest.length % 2 == 0, "even number");
    if (rest.length == 0) {
      return new PairLists.SingletonImmutablePairList<>(t, u);
    }
    Object[] elements = new Object[rest.length + 2];
    elements[0] = t;
    elements[1] = u;
    System.arraycopy(rest, 0, elements, 2, rest.length);
    return new PairLists.ArrayImmutablePairList<>(elements);
  }

  /** Creates an ImmutablePairList whose contents are a copy of a given
   * collection. */
  @SuppressWarnings("unchecked")
  static  ImmutablePairList copyOf(
      Iterable> iterable) {
    // Every PairList - mutable and immutable - knows how to quickly make
    // itself immutable.
    if (iterable instanceof PairList) {
      return ((PairList) iterable).immutable();
    }

    // If it's a collection, we know its size, and therefore can create an
    // array directly, without an intermediate ArrayList.
    if (iterable instanceof Collection) {
      final Collection> collection =
          (Collection>) iterable;
      switch (collection.size()) {
      case 0:
        return of();

      case 1:
        // Use of iterator is suboptimal. If we knew this was a list we could
        // call get(0), but the special case doesn't seem worth the effort.
        final Map.Entry entry = iterable.iterator().next();
        return of(entry.getKey(), entry.getValue());

      default:
        Object[] elements = new Object[2 * collection.size()];
        int i = 0;
        for (Map.Entry entry2 : iterable) {
          elements[i++] = entry2.getKey();
          elements[i++] = entry2.getValue();
        }
        return new PairLists.ArrayImmutablePairList<>(elements);
      }
    }

    // Not a collection, so we don't know its size in advance.
    final List