Fix algorithm generics.

lib/src/algorithms.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import "dart:math" as math;
 
-/// Version of [binarySearch] optimized for comparable keys
-int _comparableBinarySearch/*<T extends Comparable<T>>*/(
-    List<Comparable/*<T>*/> list, Comparable/*<T>*/ value) {
-  int min = 0;
-  int max = list.length;
-  while (min < max) {
-    int mid = min + ((max - min) >> 1);
-    var element = list[mid];
-    int comp = element.compareTo(value);
-    if (comp == 0) return mid;
-    if (comp < 0) {
-      min = mid + 1;
-    } else {
-      max = mid;
-    }
-  }
-  return -1;
-}
+import "utils.dart";
 
 /// Returns a position of the [value] in [sortedList], if it is there.
 ///
 /// If the list isn't sorted according to the [compare] function, the result
 /// is unpredictable.
 ///
-/// If [compare] is omitted, it defaults to calling [Comparable.compareTo] on
-/// the objects.
+/// If [compare] is omitted, this defaults to calling [Comparable.compareTo] on
+/// the objects. If any object is not [Comparable], this throws a [CastError].
 ///
 /// Returns -1 if [value] is not in the list by default.
-int binarySearch/*<T extends Comparable<T>>*/(
-    List/*<T>*/ sortedList, /*=T*/ value, { int compare(/*=T*/ a, /*=T*/ b) }) {
-  if (compare == null) {
-    return _comparableBinarySearch(sortedList, value);
-  }
+int binarySearch/*<T>*/(List/*<T>*/ sortedList, /*=T*/ value,
+    {int compare(/*=T*/ a, /*=T*/ b)}) {
+  compare ??= defaultCompare/*<T>*/();
   int min = 0;
   int max = sortedList.length;
   while (min < max) {
     int mid = min + ((max - min) >> 1);
     var element = sortedList[mid];
     int comp = compare(element, value);
     if (comp == 0) return mid;
     if (comp < 0) {
       min = mid + 1;
     } else {
       max = mid;
     }
   }
   return -1;
 }
 
-/// Version of [lowerBound] optimized for comparable keys
-int _comparableLowerBound(List<Comparable> list, Comparable value) {
-  int min = 0;
-  int max = list.length;
-  while (min < max) {
-    int mid = min + ((max - min) >> 1);
-    var element = list[mid];
-    int comp = element.compareTo(value);
-    if (comp < 0) {
-      min = mid + 1;
-    } else {
-      max = mid;
-    }
-  }
-  return min;
-}
-
 /// Returns the first position in [sortedList] that does not compare less than
 /// [value].
 ///
 /// If the list isn't sorted according to the [compare] function, the result
 /// is unpredictable.
 ///
-/// If [compare] is omitted, it defaults to calling [Comparable.compareTo] on
-/// the objects.
+/// If [compare] is omitted, this defaults to calling [Comparable.compareTo] on
+/// the objects. If any object is not [Comparable], this throws a [CastError].
 ///
 /// Returns [sortedList.length] if all the items in [sortedList] compare less
 /// than [value].
-int lowerBound/*<T extends Comparable<T>>*/(
-    List/*<T>*/ sortedList, /*=T*/ value, { int compare(/*=T*/ a, /*=T*/ b) }) {
-  if (compare == null) {
-    return _comparableLowerBound(sortedList, value);
-  }
+int lowerBound/*<T>*/(List/*<T>*/ sortedList, /*=T*/ value,
+    {int compare(/*=T*/ a, /*=T*/ b)}) {
+  compare ??= defaultCompare/*<T>*/();
   int min = 0;
   int max = sortedList.length;
   while (min < max) {
     int mid = min + ((max - min) >> 1);
     var element = sortedList[mid];
     int comp = compare(element, value);
     if (comp < 0) {
       min = mid + 1;
     } else {
       max = mid;
@@ skipping 27 matching lines @@
 
 /// Internal helper function that assumes valid arguments.
 void _reverse(List list, int start, int end) {
   for (int i = start, j = end - 1; i < j; i++, j--) {
     var tmp = list[i];
     list[i] = list[j];
     list[j] = tmp;
   }
 }
 
-/// Sort a list using insertion sort.
+/// Sort a list between [start] (inclusive) and [end] (exclusive) using
+/// insertion sort.
+///
+/// If [compare] is omitted, this defaults to calling [Comparable.compareTo] on
+/// the objects. If any object is not [Comparable], this throws a [CastError].
 ///
 /// Insertion sort is a simple sorting algorithm. For `n` elements it does on
 /// the order of `n * log(n)` comparisons but up to `n` squared moves. The
 /// sorting is performed in-place, without using extra memory.
 ///
 /// For short lists the many moves have less impact than the simple algorithm,
 /// and it is often the favored sorting algorithm for short lists.
 ///
 /// This insertion sort is stable: Equal elements end up in the same order
 /// as they started in.
-void insertionSort(List list,
-                   { int compare(a, b),
-                     int start: 0,
-                     int end: null }) {
+void insertionSort/*<T>*/(List/*<T>*/ list, {int compare(/*=T*/ a, /*=T*/ b),
+    int start: 0, int end}) {
   // If the same method could have both positional and named optional
   // parameters, this should be (list, [start, end], {compare}).
-  if (end == null) end = list.length;
-  if (compare == null) compare = Comparable.compare;
-  _insertionSort(list, compare, start, end, start + 1);
-}
+  compare ??= defaultCompare/*<T>*/();
+  end ??= list.length;
 
-/// Internal helper function that assumes arguments correct.
-///
-/// Assumes that the elements up to [sortedUntil] (not inclusive) are
-/// already sorted. The [sortedUntil] values should always be at least
-/// `start + 1`.
-void _insertionSort(List list, int compare(a, b), int start, int end,
-                    int sortedUntil) {
-  for (int pos = sortedUntil; pos < end; pos++) {
+  for (int pos = start + 1; pos < end; pos++) {
     int min = start;
     int max = pos;
     var element = list[pos];
     while (min < max) {
       int mid = min + ((max - min) >> 1);
       int comparison = compare(element, list[mid]);
       if (comparison < 0) {
         max = mid;
       } else {
         min = mid + 1;
       }
     }
     list.setRange(min + 1, pos + 1, list, min);
     list[min] = element;
   }
 }
 
 /// Limit below which merge sort defaults to insertion sort.
 const int _MERGE_SORT_LIMIT = 32;
 
-/// Sorts a list, or a range of a list, using the merge sort algorithm.
+/// Sorts a list between [start] (inclusive) and [end] (exclusive) using the
+/// merge sort algorithm.
+///
+/// If [compare] is omitted, this defaults to calling [Comparable.compareTo] on
+/// the objects. If any object is not [Comparable], this throws a [CastError].
 ///
 /// Merge-sorting works by splitting the job into two parts, sorting each
 /// recursively, and then merging the two sorted parts.
 ///
 /// This takes on the order of `n * log(n)` comparisons and moves to sort
 /// `n` elements, but requires extra space of about the same size as the list
 /// being sorted.
 ///
 /// This merge sort is stable: Equal elements end up in the same order
 /// as they started in.
-void mergeSort(List list, {int start: 0, int end: null, int compare(a, b)}) {
-  if (end == null) end = list.length;
-  if (compare == null) compare = Comparable.compare;
+void mergeSort/*<T>*/(List/*<T>*/ list, {int start: 0, int end,
+    int compare(/*=T*/ a, /*=T*/ b)}) {
+  end ??= list.length;
+  compare ??= defaultCompare/*<T>*/();
+
   int length = end - start;
   if (length < 2) return;
   if (length < _MERGE_SORT_LIMIT) {
-    _insertionSort(list, compare, start, end, start + 1);
+    insertionSort(list, compare: compare, start: start, end: end);
     return;
   }
   // Special case the first split instead of directly calling
   // _mergeSort, because the _mergeSort requires its target to
   // be different from its source, and it requires extra space
   // of the same size as the list to sort.
   // This split allows us to have only half as much extra space,
   // and it ends up in the original place.
   int middle = start + ((end - start) >> 1);
   int firstLength = middle - start;
   int secondLength = end - middle;
   // secondLength is always the same as firstLength, or one greater.
-  List scratchSpace = new List(secondLength);
+  var scratchSpace = new List<T>(secondLength);
   _mergeSort(list, compare, middle, end, scratchSpace, 0);
   int firstTarget = end - firstLength;
   _mergeSort(list, compare, start, middle, list, firstTarget);
   _merge(compare,
          list, firstTarget, end,
          scratchSpace, 0, secondLength,
          list, start);
 }
 
 /// Performs an insertion sort into a potentially different list than the
 /// one containing the original values.
 ///
 /// It will work in-place as well.
-void _movingInsertionSort(List list, int compare(a, b), int start, int end,
-                          List target, int targetOffset) {
+void _movingInsertionSort/*<T>*/(List/*<T>*/ list,
+    int compare(/*=T*/ a, /*=T*/ b), int start, int end, List/*<T>*/ target,
+    int targetOffset) {
   int length = end - start;
   if (length == 0) return;
   target[targetOffset] = list[start];
   for (int i = 1; i < length; i++) {
     var element = list[start + i];
     int min = targetOffset;
     int max = targetOffset + i;
     while (min < max) {
       int mid = min + ((max - min) >> 1);
       if (compare(element, target[mid]) < 0) {
         max = mid;
       } else {
         min = mid + 1;
       }
     }
     target.setRange(min + 1, targetOffset + i + 1,
                     target, min);
     target[min] = element;
   }
 }
 
 /// Sorts [list] from [start] to [end] into [target] at [targetOffset].
 ///
 /// The `target` list must be able to contain the range from `start` to `end`
 /// after `targetOffset`.
 ///
 /// Allows target to be the same list as [list], as long as it's not
 /// overlapping the `start..end` range.
-void _mergeSort(List list, int compare(a, b), int start, int end,
-                List target, int targetOffset) {
+void _mergeSort/*<T>*/(List/*<T>*/ list, int compare(/*=T*/ a, /*=T*/ b),
+    int start, int end, List/*<T>*/ target, int targetOffset) {
   int length = end - start;
   if (length < _MERGE_SORT_LIMIT) {
     _movingInsertionSort(list, compare, start, end, target, targetOffset);
     return;
   }
   int middle = start + (length >> 1);
   int firstLength = middle - start;
   int secondLength = end - middle;
   // Here secondLength >= firstLength (differs by at most one).
   int targetMiddle = targetOffset + firstLength;
@@ skipping 11 matching lines @@
 }
 
 /// Merges two lists into a target list.
 ///
 /// One of the input lists may be positioned at the end of the target
 /// list.
 ///
 /// For equal object, elements from [firstList] are always preferred.
 /// This allows the merge to be stable if the first list contains elements
 /// that started out earlier than the ones in [secondList]
-void _merge(int compare(a, b),
-            List firstList, int firstStart, int firstEnd,
-            List secondList, int secondStart, int secondEnd,
-            List target, int targetOffset) {
+void _merge/*<T>*/(int compare(/*=T*/ a, /*=T*/ b),
+    List/*<T>*/ firstList, int firstStart, int firstEnd,
+    List/*<T>*/ secondList, int secondStart, int secondEnd,
+    List/*<T>*/ target, int targetOffset) {
   // No empty lists reaches here.
   assert(firstStart < firstEnd);
   assert(secondStart < secondEnd);
   int cursor1 = firstStart;
   int cursor2 = secondStart;
   var firstElement = firstList[cursor1++];
   var secondElement = secondList[cursor2++];
   while (true) {
     if (compare(firstElement, secondElement) <= 0) {
       target[targetOffset++] = firstElement;
@@ skipping 10 matching lines @@
       target.setRange(targetOffset, targetOffset + (firstEnd - cursor1),
           firstList, cursor1);
       return;
     }
   }
   // First list empties first. Reached by break above.
   target[targetOffset++] = secondElement;
   target.setRange(targetOffset, targetOffset + (secondEnd - cursor2),
       secondList, cursor2);
 }