001/*
002 * Copyright (C) 2008 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.collect;
018
019import static com.google.common.base.Preconditions.checkArgument;
020import static com.google.common.base.Preconditions.checkNotNull;
021
022import com.google.common.annotations.GwtCompatible;
023import com.google.common.annotations.GwtIncompatible;
024import com.google.common.annotations.J2ktIncompatible;
025import com.google.common.base.Equivalence;
026import com.google.common.base.Predicate;
027import com.google.errorprone.annotations.Immutable;
028import com.google.errorprone.annotations.InlineMe;
029import java.io.Serializable;
030import java.util.Comparator;
031import java.util.Iterator;
032import java.util.NoSuchElementException;
033import java.util.SortedSet;
034import org.jspecify.annotations.Nullable;
035
036/**
037 * A range (or "interval") defines the <i>boundaries</i> around a contiguous span of values of some
038 * {@code Comparable} type; for example, "integers from 1 to 100 inclusive." Note that it is not
039 * possible to <i>iterate</i> over these contained values. To do so, pass this range instance and an
040 * appropriate {@link DiscreteDomain} to {@link ContiguousSet#create}.
041 *
042 * <h2>Types of ranges</h2>
043 *
044 * <p>Each end of the range may be bounded or unbounded. If bounded, there is an associated
045 * <i>endpoint</i> value, and the range is considered to be either <i>open</i> (does not include the
046 * endpoint) or <i>closed</i> (includes the endpoint) on that side. With three possibilities on each
047 * side, this yields nine basic types of ranges, enumerated below. (Notation: a square bracket
048 * ({@code [ ]}) indicates that the range is closed on that side; a parenthesis ({@code ( )}) means
049 * it is either open or unbounded. The construct {@code {x | statement}} is read "the set of all
050 * <i>x</i> such that <i>statement</i>.")
051 *
052 * <blockquote>
053 *
054 * <table>
055 * <caption>Range Types</caption>
056 * <tr><th>Notation        <th>Definition               <th>Factory method
057 * <tr><td>{@code (a..b)}  <td>{@code {x | a < x < b}}  <td>{@link Range#open open}
058 * <tr><td>{@code [a..b]}  <td>{@code {x | a <= x <= b}}<td>{@link Range#closed closed}
059 * <tr><td>{@code (a..b]}  <td>{@code {x | a < x <= b}} <td>{@link Range#openClosed openClosed}
060 * <tr><td>{@code [a..b)}  <td>{@code {x | a <= x < b}} <td>{@link Range#closedOpen closedOpen}
061 * <tr><td>{@code (a..+∞)} <td>{@code {x | x > a}}      <td>{@link Range#greaterThan greaterThan}
062 * <tr><td>{@code [a..+∞)} <td>{@code {x | x >= a}}     <td>{@link Range#atLeast atLeast}
063 * <tr><td>{@code (-∞..b)} <td>{@code {x | x < b}}      <td>{@link Range#lessThan lessThan}
064 * <tr><td>{@code (-∞..b]} <td>{@code {x | x <= b}}     <td>{@link Range#atMost atMost}
065 * <tr><td>{@code (-∞..+∞)}<td>{@code {x}}              <td>{@link Range#all all}
066 * </table>
067 *
068 * </blockquote>
069 *
070 * <p>When both endpoints exist, the upper endpoint may not be less than the lower. The endpoints
071 * may be equal only if at least one of the bounds is closed:
072 *
073 * <ul>
074 *   <li>{@code [a..a]} : a singleton range
075 *   <li>{@code [a..a); (a..a]} : {@linkplain #isEmpty empty} ranges; also valid
076 *   <li>{@code (a..a)} : <b>invalid</b>; an exception will be thrown
077 * </ul>
078 *
079 * <h2>Warnings</h2>
080 *
081 * <ul>
082 *   <li>Use immutable value types only, if at all possible. If you must use a mutable type, <b>do
083 *       not</b> allow the endpoint instances to mutate after the range is created!
084 *   <li>Your value type's comparison method should be {@linkplain Comparable consistent with
085 *       equals} if at all possible. Otherwise, be aware that concepts used throughout this
086 *       documentation such as "equal", "same", "unique" and so on actually refer to whether {@link
087 *       Comparable#compareTo compareTo} returns zero, not whether {@link Object#equals equals}
088 *       returns {@code true}.
089 *   <li>A class which implements {@code Comparable<UnrelatedType>} is very broken, and will cause
090 *       undefined horrible things to happen in {@code Range}. For now, the Range API does not
091 *       prevent its use, because this would also rule out all ungenerified (pre-JDK1.5) data types.
092 *       <b>This may change in the future.</b>
093 * </ul>
094 *
095 * <h2>Other notes</h2>
096 *
097 * <ul>
098 *   <li>All ranges are shallow-immutable.
099 *   <li>Instances of this type are obtained using the static factory methods in this class.
100 *   <li>Ranges are <i>convex</i>: whenever two values are contained, all values in between them
101 *       must also be contained. More formally, for any {@code c1 <= c2 <= c3} of type {@code C},
102 *       {@code r.contains(c1) && r.contains(c3)} implies {@code r.contains(c2)}). This means that a
103 *       {@code Range<Integer>} can never be used to represent, say, "all <i>prime</i> numbers from
104 *       1 to 100."
105 *   <li>When evaluated as a {@link Predicate}, a range yields the same result as invoking {@link
106 *       #contains}.
107 *   <li>Terminology note: a range {@code a} is said to be the <i>maximal</i> range having property
108 *       <i>P</i> if, for all ranges {@code b} also having property <i>P</i>, {@code a.encloses(b)}.
109 *       Likewise, {@code a} is <i>minimal</i> when {@code b.encloses(a)} for all {@code b} having
110 *       property <i>P</i>. See, for example, the definition of {@link #intersection intersection}.
111 *   <li>A {@code Range} is serializable if it has no bounds, or if each bound is serializable.
112 * </ul>
113 *
114 * <h2>Further reading</h2>
115 *
116 * <p>See the Guava User Guide article on <a
117 * href="https://github.com/google/guava/wiki/RangesExplained">{@code Range}</a>.
118 *
119 * @author Kevin Bourrillion
120 * @author Gregory Kick
121 * @since 10.0
122 */
123@GwtCompatible
124@SuppressWarnings("rawtypes") // https://github.com/google/guava/issues/989
125@Immutable(containerOf = "C")
126public final class Range<C extends Comparable> implements Predicate<C>, Serializable {
127  @SuppressWarnings("unchecked")
128  static <C extends Comparable<?>> Ordering<Range<C>> rangeLexOrdering() {
129    return (Ordering<Range<C>>) RangeLexOrdering.INSTANCE;
130  }
131
132  static <C extends Comparable<?>> Range<C> create(Cut<C> lowerBound, Cut<C> upperBound) {
133    return new Range<>(lowerBound, upperBound);
134  }
135
136  /**
137   * Returns a range that contains all values strictly greater than {@code lower} and strictly less
138   * than {@code upper}.
139   *
140   * @throws IllegalArgumentException if {@code lower} is greater than <i>or equal to</i> {@code
141   *     upper}
142   * @throws ClassCastException if {@code lower} and {@code upper} are not mutually comparable
143   * @since 14.0
144   */
145  public static <C extends Comparable<?>> Range<C> open(C lower, C upper) {
146    return create(Cut.aboveValue(lower), Cut.belowValue(upper));
147  }
148
149  /**
150   * Returns a range that contains all values greater than or equal to {@code lower} and less than
151   * or equal to {@code upper}.
152   *
153   * @throws IllegalArgumentException if {@code lower} is greater than {@code upper}
154   * @throws ClassCastException if {@code lower} and {@code upper} are not mutually comparable
155   * @since 14.0
156   */
157  public static <C extends Comparable<?>> Range<C> closed(C lower, C upper) {
158    return create(Cut.belowValue(lower), Cut.aboveValue(upper));
159  }
160
161  /**
162   * Returns a range that contains all values greater than or equal to {@code lower} and strictly
163   * less than {@code upper}.
164   *
165   * @throws IllegalArgumentException if {@code lower} is greater than {@code upper}
166   * @throws ClassCastException if {@code lower} and {@code upper} are not mutually comparable
167   * @since 14.0
168   */
169  public static <C extends Comparable<?>> Range<C> closedOpen(C lower, C upper) {
170    return create(Cut.belowValue(lower), Cut.belowValue(upper));
171  }
172
173  /**
174   * Returns a range that contains all values strictly greater than {@code lower} and less than or
175   * equal to {@code upper}.
176   *
177   * @throws IllegalArgumentException if {@code lower} is greater than {@code upper}
178   * @throws ClassCastException if {@code lower} and {@code upper} are not mutually comparable
179   * @since 14.0
180   */
181  public static <C extends Comparable<?>> Range<C> openClosed(C lower, C upper) {
182    return create(Cut.aboveValue(lower), Cut.aboveValue(upper));
183  }
184
185  /**
186   * Returns a range that contains any value from {@code lower} to {@code upper}, where each
187   * endpoint may be either inclusive (closed) or exclusive (open).
188   *
189   * @throws IllegalArgumentException if {@code lower} is greater than {@code upper}
190   * @throws ClassCastException if {@code lower} and {@code upper} are not mutually comparable
191   * @since 14.0
192   */
193  public static <C extends Comparable<?>> Range<C> range(
194      C lower, BoundType lowerType, C upper, BoundType upperType) {
195    checkNotNull(lowerType);
196    checkNotNull(upperType);
197
198    Cut<C> lowerBound =
199        (lowerType == BoundType.OPEN) ? Cut.aboveValue(lower) : Cut.belowValue(lower);
200    Cut<C> upperBound =
201        (upperType == BoundType.OPEN) ? Cut.belowValue(upper) : Cut.aboveValue(upper);
202    return create(lowerBound, upperBound);
203  }
204
205  /**
206   * Returns a range that contains all values strictly less than {@code endpoint}.
207   *
208   * @since 14.0
209   */
210  public static <C extends Comparable<?>> Range<C> lessThan(C endpoint) {
211    return create(Cut.belowAll(), Cut.belowValue(endpoint));
212  }
213
214  /**
215   * Returns a range that contains all values less than or equal to {@code endpoint}.
216   *
217   * @since 14.0
218   */
219  public static <C extends Comparable<?>> Range<C> atMost(C endpoint) {
220    return create(Cut.belowAll(), Cut.aboveValue(endpoint));
221  }
222
223  /**
224   * Returns a range with no lower bound up to the given endpoint, which may be either inclusive
225   * (closed) or exclusive (open).
226   *
227   * @since 14.0
228   */
229  public static <C extends Comparable<?>> Range<C> upTo(C endpoint, BoundType boundType) {
230    switch (boundType) {
231      case OPEN:
232        return lessThan(endpoint);
233      case CLOSED:
234        return atMost(endpoint);
235    }
236    throw new AssertionError();
237  }
238
239  /**
240   * Returns a range that contains all values strictly greater than {@code endpoint}.
241   *
242   * @since 14.0
243   */
244  public static <C extends Comparable<?>> Range<C> greaterThan(C endpoint) {
245    return create(Cut.aboveValue(endpoint), Cut.aboveAll());
246  }
247
248  /**
249   * Returns a range that contains all values greater than or equal to {@code endpoint}.
250   *
251   * @since 14.0
252   */
253  public static <C extends Comparable<?>> Range<C> atLeast(C endpoint) {
254    return create(Cut.belowValue(endpoint), Cut.aboveAll());
255  }
256
257  /**
258   * Returns a range from the given endpoint, which may be either inclusive (closed) or exclusive
259   * (open), with no upper bound.
260   *
261   * @since 14.0
262   */
263  public static <C extends Comparable<?>> Range<C> downTo(C endpoint, BoundType boundType) {
264    switch (boundType) {
265      case OPEN:
266        return greaterThan(endpoint);
267      case CLOSED:
268        return atLeast(endpoint);
269    }
270    throw new AssertionError();
271  }
272
273  private static final Range<Comparable> ALL = new Range<>(Cut.belowAll(), Cut.aboveAll());
274
275  /**
276   * Returns a range that contains every value of type {@code C}.
277   *
278   * @since 14.0
279   */
280  @SuppressWarnings("unchecked")
281  public static <C extends Comparable<?>> Range<C> all() {
282    return (Range) ALL;
283  }
284
285  /**
286   * Returns a range that {@linkplain Range#contains(Comparable) contains} only the given value. The
287   * returned range is {@linkplain BoundType#CLOSED closed} on both ends.
288   *
289   * @since 14.0
290   */
291  public static <C extends Comparable<?>> Range<C> singleton(C value) {
292    return closed(value, value);
293  }
294
295  /**
296   * Returns the minimal range that {@linkplain Range#contains(Comparable) contains} all of the
297   * given values. The returned range is {@linkplain BoundType#CLOSED closed} on both ends.
298   *
299   * @throws ClassCastException if the values are not mutually comparable
300   * @throws NoSuchElementException if {@code values} is empty
301   * @throws NullPointerException if any of {@code values} is null
302   * @since 14.0
303   */
304  public static <C extends Comparable<?>> Range<C> encloseAll(Iterable<C> values) {
305    checkNotNull(values);
306    if (values instanceof SortedSet) {
307      SortedSet<C> set = (SortedSet<C>) values;
308      Comparator<?> comparator = set.comparator();
309      if (Ordering.<C>natural().equals(comparator) || comparator == null) {
310        return closed(set.first(), set.last());
311      }
312    }
313    Iterator<C> valueIterator = values.iterator();
314    C min = checkNotNull(valueIterator.next());
315    C max = min;
316    while (valueIterator.hasNext()) {
317      C value = checkNotNull(valueIterator.next());
318      min = Ordering.<C>natural().min(min, value);
319      max = Ordering.<C>natural().max(max, value);
320    }
321    return closed(min, max);
322  }
323
324  final Cut<C> lowerBound;
325  final Cut<C> upperBound;
326
327  private Range(Cut<C> lowerBound, Cut<C> upperBound) {
328    this.lowerBound = checkNotNull(lowerBound);
329    this.upperBound = checkNotNull(upperBound);
330    if (lowerBound.compareTo(upperBound) > 0
331        || lowerBound == Cut.<C>aboveAll()
332        || upperBound == Cut.<C>belowAll()) {
333      throw new IllegalArgumentException("Invalid range: " + toString(lowerBound, upperBound));
334    }
335  }
336
337  /** Returns {@code true} if this range has a lower endpoint. */
338  public boolean hasLowerBound() {
339    return lowerBound != Cut.belowAll();
340  }
341
342  /**
343   * Returns the lower endpoint of this range.
344   *
345   * @throws IllegalStateException if this range is unbounded below (that is, {@link
346   *     #hasLowerBound()} returns {@code false})
347   */
348  public C lowerEndpoint() {
349    return lowerBound.endpoint();
350  }
351
352  /**
353   * Returns the type of this range's lower bound: {@link BoundType#CLOSED} if the range includes
354   * its lower endpoint, {@link BoundType#OPEN} if it does not.
355   *
356   * @throws IllegalStateException if this range is unbounded below (that is, {@link
357   *     #hasLowerBound()} returns {@code false})
358   */
359  public BoundType lowerBoundType() {
360    return lowerBound.typeAsLowerBound();
361  }
362
363  /** Returns {@code true} if this range has an upper endpoint. */
364  public boolean hasUpperBound() {
365    return upperBound != Cut.aboveAll();
366  }
367
368  /**
369   * Returns the upper endpoint of this range.
370   *
371   * @throws IllegalStateException if this range is unbounded above (that is, {@link
372   *     #hasUpperBound()} returns {@code false})
373   */
374  public C upperEndpoint() {
375    return upperBound.endpoint();
376  }
377
378  /**
379   * Returns the type of this range's upper bound: {@link BoundType#CLOSED} if the range includes
380   * its upper endpoint, {@link BoundType#OPEN} if it does not.
381   *
382   * @throws IllegalStateException if this range is unbounded above (that is, {@link
383   *     #hasUpperBound()} returns {@code false})
384   */
385  public BoundType upperBoundType() {
386    return upperBound.typeAsUpperBound();
387  }
388
389  /**
390   * Returns {@code true} if this range is of the form {@code [v..v)} or {@code (v..v]}. (This does
391   * not encompass ranges of the form {@code (v..v)}, because such ranges are <i>invalid</i> and
392   * can't be constructed at all.)
393   *
394   * <p>Note that certain discrete ranges such as the integer range {@code (3..4)} are <b>not</b>
395   * considered empty, even though they contain no actual values. In these cases, it may be helpful
396   * to preprocess ranges with {@link #canonical(DiscreteDomain)}.
397   */
398  public boolean isEmpty() {
399    return lowerBound.equals(upperBound);
400  }
401
402  /**
403   * Returns {@code true} if {@code value} is within the bounds of this range. For example, on the
404   * range {@code [0..2)}, {@code contains(1)} returns {@code true}, while {@code contains(2)}
405   * returns {@code false}.
406   */
407  public boolean contains(C value) {
408    checkNotNull(value);
409    // let this throw CCE if there is some trickery going on
410    return lowerBound.isLessThan(value) && !upperBound.isLessThan(value);
411  }
412
413  /**
414   * @deprecated Provided only to satisfy the {@link Predicate} interface; use {@link #contains}
415   *     instead.
416   */
417  @InlineMe(replacement = "this.contains(input)")
418  @Deprecated
419  @Override
420  public boolean apply(C input) {
421    return contains(input);
422  }
423
424  /**
425   * @deprecated Provided only to satisfy the {@link java.util.function.Predicate} interface; use
426   *     {@link #contains} instead.
427   * @since 21.0
428   */
429  @InlineMe(replacement = "this.contains(input)")
430  @Deprecated
431  @Override
432  public boolean test(C input) {
433    return contains(input);
434  }
435
436  /**
437   * Returns {@code true} if every element in {@code values} is {@linkplain #contains contained} in
438   * this range.
439   */
440  public boolean containsAll(Iterable<? extends C> values) {
441    if (Iterables.isEmpty(values)) {
442      return true;
443    }
444
445    // this optimizes testing equality of two range-backed sets
446    if (values instanceof SortedSet) {
447      SortedSet<? extends C> set = (SortedSet<? extends C>) values;
448      Comparator<?> comparator = set.comparator();
449      if (Ordering.natural().equals(comparator) || comparator == null) {
450        return contains(set.first()) && contains(set.last());
451      }
452    }
453
454    for (C value : values) {
455      if (!contains(value)) {
456        return false;
457      }
458    }
459    return true;
460  }
461
462  /**
463   * Returns {@code true} if the bounds of {@code other} do not extend outside the bounds of this
464   * range. Examples:
465   *
466   * <ul>
467   *   <li>{@code [3..6]} encloses {@code [4..5]}
468   *   <li>{@code (3..6)} encloses {@code (3..6)}
469   *   <li>{@code [3..6]} encloses {@code [4..4)} (even though the latter is empty)
470   *   <li>{@code (3..6]} does not enclose {@code [3..6]}
471   *   <li>{@code [4..5]} does not enclose {@code (3..6)} (even though it contains every value
472   *       contained by the latter range)
473   *   <li>{@code [3..6]} does not enclose {@code (1..1]} (even though it contains every value
474   *       contained by the latter range)
475   * </ul>
476   *
477   * <p>Note that if {@code a.encloses(b)}, then {@code b.contains(v)} implies {@code
478   * a.contains(v)}, but as the last two examples illustrate, the converse is not always true.
479   *
480   * <p>Being reflexive, antisymmetric and transitive, the {@code encloses} relation defines a
481   * <i>partial order</i> over ranges. There exists a unique {@linkplain Range#all maximal} range
482   * according to this relation, and also numerous {@linkplain #isEmpty minimal} ranges. Enclosure
483   * also implies {@linkplain #isConnected connectedness}.
484   */
485  public boolean encloses(Range<C> other) {
486    return lowerBound.compareTo(other.lowerBound) <= 0
487        && upperBound.compareTo(other.upperBound) >= 0;
488  }
489
490  /**
491   * Returns {@code true} if there exists a (possibly empty) range which is {@linkplain #encloses
492   * enclosed} by both this range and {@code other}.
493   *
494   * <p>For example,
495   *
496   * <ul>
497   *   <li>{@code [2, 4)} and {@code [5, 7)} are not connected
498   *   <li>{@code [2, 4)} and {@code [3, 5)} are connected, because both enclose {@code [3, 4)}
499   *   <li>{@code [2, 4)} and {@code [4, 6)} are connected, because both enclose the empty range
500   *       {@code [4, 4)}
501   * </ul>
502   *
503   * <p>Note that this range and {@code other} have a well-defined {@linkplain #span union} and
504   * {@linkplain #intersection intersection} (as a single, possibly-empty range) if and only if this
505   * method returns {@code true}.
506   *
507   * <p>The connectedness relation is both reflexive and symmetric, but does not form an {@linkplain
508   * Equivalence equivalence relation} as it is not transitive.
509   *
510   * <p>Note that certain discrete ranges are not considered connected, even though there are no
511   * elements "between them." For example, {@code [3, 5]} is not considered connected to {@code [6,
512   * 10]}. In these cases, it may be desirable for both input ranges to be preprocessed with {@link
513   * #canonical(DiscreteDomain)} before testing for connectedness.
514   */
515  public boolean isConnected(Range<C> other) {
516    return lowerBound.compareTo(other.upperBound) <= 0
517        && other.lowerBound.compareTo(upperBound) <= 0;
518  }
519
520  /**
521   * Returns the maximal range {@linkplain #encloses enclosed} by both this range and {@code
522   * connectedRange}, if such a range exists.
523   *
524   * <p>For example, the intersection of {@code [1..5]} and {@code (3..7)} is {@code (3..5]}. The
525   * resulting range may be empty; for example, {@code [1..5)} intersected with {@code [5..7)}
526   * yields the empty range {@code [5..5)}.
527   *
528   * <p>The intersection exists if and only if the two ranges are {@linkplain #isConnected
529   * connected}.
530   *
531   * <p>The intersection operation is commutative, associative and idempotent, and its identity
532   * element is {@link Range#all}).
533   *
534   * @throws IllegalArgumentException if {@code isConnected(connectedRange)} is {@code false}
535   */
536  public Range<C> intersection(Range<C> connectedRange) {
537    int lowerCmp = lowerBound.compareTo(connectedRange.lowerBound);
538    int upperCmp = upperBound.compareTo(connectedRange.upperBound);
539    if (lowerCmp >= 0 && upperCmp <= 0) {
540      return this;
541    } else if (lowerCmp <= 0 && upperCmp >= 0) {
542      return connectedRange;
543    } else {
544      Cut<C> newLower = (lowerCmp >= 0) ? lowerBound : connectedRange.lowerBound;
545      Cut<C> newUpper = (upperCmp <= 0) ? upperBound : connectedRange.upperBound;
546
547      // create() would catch this, but give a confusing error message
548      checkArgument(
549          newLower.compareTo(newUpper) <= 0,
550          "intersection is undefined for disconnected ranges %s and %s",
551          this,
552          connectedRange);
553
554      // TODO(kevinb): all the precondition checks in the constructor are redundant...
555      return create(newLower, newUpper);
556    }
557  }
558
559  /**
560   * Returns the maximal range lying between this range and {@code otherRange}, if such a range
561   * exists. The resulting range may be empty if the two ranges are adjacent but non-overlapping.
562   *
563   * <p>For example, the gap of {@code [1..5]} and {@code (7..10)} is {@code (5..7]}. The resulting
564   * range may be empty; for example, the gap between {@code [1..5)} {@code [5..7)} yields the empty
565   * range {@code [5..5)}.
566   *
567   * <p>The gap exists if and only if the two ranges are either disconnected or immediately adjacent
568   * (any intersection must be an empty range).
569   *
570   * <p>The gap operation is commutative.
571   *
572   * @throws IllegalArgumentException if this range and {@code otherRange} have a nonempty
573   *     intersection
574   * @since 27.0
575   */
576  public Range<C> gap(Range<C> otherRange) {
577    /*
578     * For an explanation of the basic principle behind this check, see
579     * https://stackoverflow.com/a/35754308/28465
580     *
581     * In that explanation's notation, our `overlap` check would be `x1 < y2 && y1 < x2`. We've
582     * flipped one part of the check so that we're using "less than" in both cases (rather than a
583     * mix of "less than" and "greater than"). We've also switched to "strictly less than" rather
584     * than "less than or equal to" because of *handwave* the difference between "endpoints of
585     * inclusive ranges" and "Cuts."
586     */
587    if (lowerBound.compareTo(otherRange.upperBound) < 0
588        && otherRange.lowerBound.compareTo(upperBound) < 0) {
589      throw new IllegalArgumentException(
590          "Ranges have a nonempty intersection: " + this + ", " + otherRange);
591    }
592
593    boolean isThisFirst = this.lowerBound.compareTo(otherRange.lowerBound) < 0;
594    Range<C> firstRange = isThisFirst ? this : otherRange;
595    Range<C> secondRange = isThisFirst ? otherRange : this;
596    return create(firstRange.upperBound, secondRange.lowerBound);
597  }
598
599  /**
600   * Returns the minimal range that {@linkplain #encloses encloses} both this range and {@code
601   * other}. For example, the span of {@code [1..3]} and {@code (5..7)} is {@code [1..7)}.
602   *
603   * <p><i>If</i> the input ranges are {@linkplain #isConnected connected}, the returned range can
604   * also be called their <i>union</i>. If they are not, note that the span might contain values
605   * that are not contained in either input range.
606   *
607   * <p>Like {@link #intersection(Range) intersection}, this operation is commutative, associative
608   * and idempotent. Unlike it, it is always well-defined for any two input ranges.
609   */
610  public Range<C> span(Range<C> other) {
611    int lowerCmp = lowerBound.compareTo(other.lowerBound);
612    int upperCmp = upperBound.compareTo(other.upperBound);
613    if (lowerCmp <= 0 && upperCmp >= 0) {
614      return this;
615    } else if (lowerCmp >= 0 && upperCmp <= 0) {
616      return other;
617    } else {
618      Cut<C> newLower = (lowerCmp <= 0) ? lowerBound : other.lowerBound;
619      Cut<C> newUpper = (upperCmp >= 0) ? upperBound : other.upperBound;
620      return create(newLower, newUpper);
621    }
622  }
623
624  /**
625   * Returns the canonical form of this range in the given domain. The canonical form has the
626   * following properties:
627   *
628   * <ul>
629   *   <li>equivalence: {@code a.canonical().contains(v) == a.contains(v)} for all {@code v} (in
630   *       other words, {@code ContiguousSet.create(a.canonical(domain), domain).equals(
631   *       ContiguousSet.create(a, domain))}
632   *   <li>uniqueness: unless {@code a.isEmpty()}, {@code ContiguousSet.create(a,
633   *       domain).equals(ContiguousSet.create(b, domain))} implies {@code
634   *       a.canonical(domain).equals(b.canonical(domain))}
635   *   <li>idempotence: {@code a.canonical(domain).canonical(domain).equals(a.canonical(domain))}
636   * </ul>
637   *
638   * <p>Furthermore, this method guarantees that the range returned will be one of the following
639   * canonical forms:
640   *
641   * <ul>
642   *   <li>[start..end)
643   *   <li>[start..+∞)
644   *   <li>(-∞..end) (only if type {@code C} is unbounded below)
645   *   <li>(-∞..+∞) (only if type {@code C} is unbounded below)
646   * </ul>
647   */
648  public Range<C> canonical(DiscreteDomain<C> domain) {
649    checkNotNull(domain);
650    Cut<C> lower = lowerBound.canonical(domain);
651    Cut<C> upper = upperBound.canonical(domain);
652    return (lower == lowerBound && upper == upperBound) ? this : create(lower, upper);
653  }
654
655  /**
656   * Returns {@code true} if {@code object} is a range having the same endpoints and bound types as
657   * this range. Note that discrete ranges such as {@code (1..4)} and {@code [2..3]} are <b>not</b>
658   * equal to one another, despite the fact that they each contain precisely the same set of values.
659   * Similarly, empty ranges are not equal unless they have exactly the same representation, so
660   * {@code [3..3)}, {@code (3..3]}, {@code (4..4]} are all unequal.
661   */
662  @Override
663  public boolean equals(@Nullable Object object) {
664    if (object instanceof Range) {
665      Range<?> other = (Range<?>) object;
666      return lowerBound.equals(other.lowerBound) && upperBound.equals(other.upperBound);
667    }
668    return false;
669  }
670
671  /** Returns a hash code for this range. */
672  @Override
673  public int hashCode() {
674    return lowerBound.hashCode() * 31 + upperBound.hashCode();
675  }
676
677  /**
678   * Returns a string representation of this range, such as {@code "[3..5)"} (other examples are
679   * listed in the class documentation).
680   */
681  @Override
682  public String toString() {
683    return toString(lowerBound, upperBound);
684  }
685
686  private static String toString(Cut<?> lowerBound, Cut<?> upperBound) {
687    StringBuilder sb = new StringBuilder(16);
688    lowerBound.describeAsLowerBound(sb);
689    sb.append("..");
690    upperBound.describeAsUpperBound(sb);
691    return sb.toString();
692  }
693
694  // We declare accessors so that we can use method references like `Range::lowerBound`.
695
696  Cut<C> lowerBound() {
697    return lowerBound;
698  }
699
700  Cut<C> upperBound() {
701    return upperBound;
702  }
703
704  Object readResolve() {
705    if (this.equals(ALL)) {
706      return all();
707    } else {
708      return this;
709    }
710  }
711
712  @SuppressWarnings("unchecked") // this method may throw CCE
713  static int compareOrThrow(Comparable left, Comparable right) {
714    return left.compareTo(right);
715  }
716
717  /** Needed to serialize sorted collections of Ranges. */
718  private static final class RangeLexOrdering extends Ordering<Range<?>> implements Serializable {
719    static final Ordering<?> INSTANCE = new RangeLexOrdering();
720
721    @Override
722    public int compare(Range<?> left, Range<?> right) {
723      return ComparisonChain.start()
724          .compare(left.lowerBound, right.lowerBound)
725          .compare(left.upperBound, right.upperBound)
726          .result();
727    }
728
729    @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
730  }
731
732  @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
733}