Use const references in Standard Library algorithms range adapters where possible.

Const references enforce stronger constraints and are consistent with the standard library signature. There should be no performance loss.

PiperOrigin-RevId: 504043141
Change-Id: I6c4b017665a462fc04e16f425d330fce2c3da227

1 files changed, 51 insertions, 52 deletions

diff --git a/absl/algorithm/container.h b/absl/algorithm/container.h
index 1f57dabf..c7782d4f 100644
--- a/absl/algorithm/container.h
+++ b/absl/algorithm/container.h
@@ -77,9 +77,8 @@ using ContainerIterPairType =
     decltype(std::make_pair(ContainerIter<C1>(), ContainerIter<C2>()));
 
 template <typename C>
-using ContainerDifferenceType =
-    decltype(std::distance(std::declval<ContainerIter<C>>(),
-                           std::declval<ContainerIter<C>>()));
+using ContainerDifferenceType = decltype(std::distance(
+    std::declval<ContainerIter<C>>(), std::declval<ContainerIter<C>>()));
 
 template <typename C>
 using ContainerPointerType =
@@ -97,10 +96,14 @@ using ContainerPointerType =
 // These are meant for internal use only.
 
 template <typename C>
-ContainerIter<C> c_begin(C& c) { return begin(c); }
+ContainerIter<C> c_begin(C& c) {
+  return begin(c);
+}
 
 template <typename C>
-ContainerIter<C> c_end(C& c) { return end(c); }
+ContainerIter<C> c_end(C& c) {
+  return end(c);
+}
 
 template <typename T>
 struct IsUnorderedContainer : std::false_type {};
@@ -343,8 +346,8 @@ container_algorithm_internal::ContainerDifferenceType<const C> c_count_if(
 // return the first element where two ordered containers differ. Applies `==` to
 // the first N elements of `c1` and `c2`, where N = min(size(c1), size(c2)).
 template <typename C1, typename C2>
-container_algorithm_internal::ContainerIterPairType<C1, C2>
-c_mismatch(C1& c1, C2& c2) {
+container_algorithm_internal::ContainerIterPairType<C1, C2> c_mismatch(C1& c1,
+                                                                       C2& c2) {
   auto first1 = container_algorithm_internal::c_begin(c1);
   auto last1 = container_algorithm_internal::c_end(c1);
   auto first2 = container_algorithm_internal::c_begin(c2);
@@ -365,8 +368,8 @@ c_mismatch(C1& c1, C2& c2) {
 // the function's test condition. Applies `pred`to the first N elements of `c1`
 // and `c2`, where N = min(size(c1), size(c2)).
 template <typename C1, typename C2, typename BinaryPredicate>
-container_algorithm_internal::ContainerIterPairType<C1, C2>
-c_mismatch(C1& c1, C2& c2, BinaryPredicate pred) {
+container_algorithm_internal::ContainerIterPairType<C1, C2> c_mismatch(
+    C1& c1, C2& c2, BinaryPredicate pred) {
   auto first1 = container_algorithm_internal::c_begin(c1);
   auto last1 = container_algorithm_internal::c_end(c1);
   auto first2 = container_algorithm_internal::c_begin(c2);
@@ -655,11 +658,10 @@ OutputIterator c_replace_copy(const C& c, OutputIterator result, T&& old_value,
 // some condition, and return the results within an iterator.
 template <typename C, typename OutputIterator, typename Pred, typename T>
 OutputIterator c_replace_copy_if(const C& c, OutputIterator result, Pred&& pred,
-                                 T&& new_value) {
+                                 const T& new_value) {
   return std::replace_copy_if(container_algorithm_internal::c_begin(c),
                               container_algorithm_internal::c_end(c), result,
-                              std::forward<Pred>(pred),
-                              std::forward<T>(new_value));
+                              std::forward<Pred>(pred), new_value);
 }
 
 // c_fill()
@@ -667,9 +669,9 @@ OutputIterator c_replace_copy_if(const C& c, OutputIterator result, Pred&& pred,
 // Container-based version of the <algorithm> `std::fill()` function to fill a
 // container with some value.
 template <typename C, typename T>
-void c_fill(C& c, T&& value) {
+void c_fill(C& c, const T& value) {
   std::fill(container_algorithm_internal::c_begin(c),
-            container_algorithm_internal::c_end(c), std::forward<T>(value));
+            container_algorithm_internal::c_end(c), value);
 }
 
 // c_fill_n()
@@ -677,9 +679,8 @@ void c_fill(C& c, T&& value) {
 // Container-based version of the <algorithm> `std::fill_n()` function to fill
 // the first N elements in a container with some value.
 template <typename C, typename Size, typename T>
-void c_fill_n(C& c, Size n, T&& value) {
-  std::fill_n(container_algorithm_internal::c_begin(c), n,
-              std::forward<T>(value));
+void c_fill_n(C& c, Size n, const T& value) {
+  std::fill_n(container_algorithm_internal::c_begin(c), n, value);
 }
 
 // c_generate()
@@ -716,10 +717,11 @@ container_algorithm_internal::ContainerIter<C> c_generate_n(C& c, Size n,
 // copy a container's elements while removing any elements matching the given
 // `value`.
 template <typename C, typename OutputIterator, typename T>
-OutputIterator c_remove_copy(const C& c, OutputIterator result, T&& value) {
+OutputIterator c_remove_copy(const C& c, OutputIterator result,
+                             const T& value) {
   return std::remove_copy(container_algorithm_internal::c_begin(c),
                           container_algorithm_internal::c_end(c), result,
-                          std::forward<T>(value));
+                          value);
 }
 
 // c_remove_copy_if()
@@ -1064,20 +1066,19 @@ void c_nth_element(
 // which does not compare less than `value`.
 template <typename Sequence, typename T>
 container_algorithm_internal::ContainerIter<Sequence> c_lower_bound(
-    Sequence& sequence, T&& value) {
+    Sequence& sequence, const T& value) {
   return std::lower_bound(container_algorithm_internal::c_begin(sequence),
-                          container_algorithm_internal::c_end(sequence),
-                          std::forward<T>(value));
+                          container_algorithm_internal::c_end(sequence), value);
 }
 
 // Overload of c_lower_bound() for performing a `comp` comparison other than
 // the default `operator<`.
 template <typename Sequence, typename T, typename LessThan>
 container_algorithm_internal::ContainerIter<Sequence> c_lower_bound(
-    Sequence& sequence, T&& value, LessThan&& comp) {
+    Sequence& sequence, const T& value, LessThan&& comp) {
   return std::lower_bound(container_algorithm_internal::c_begin(sequence),
-                          container_algorithm_internal::c_end(sequence),
-                          std::forward<T>(value), std::forward<LessThan>(comp));
+                          container_algorithm_internal::c_end(sequence), value,
+                          std::forward<LessThan>(comp));
 }
 
 // c_upper_bound()
@@ -1087,20 +1088,19 @@ container_algorithm_internal::ContainerIter<Sequence> c_lower_bound(
 // which is greater than `value`.
 template <typename Sequence, typename T>
 container_algorithm_internal::ContainerIter<Sequence> c_upper_bound(
-    Sequence& sequence, T&& value) {
+    Sequence& sequence, const T& value) {
   return std::upper_bound(container_algorithm_internal::c_begin(sequence),
-                          container_algorithm_internal::c_end(sequence),
-                          std::forward<T>(value));
+                          container_algorithm_internal::c_end(sequence), value);
 }
 
 // Overload of c_upper_bound() for performing a `comp` comparison other than
 // the default `operator<`.
 template <typename Sequence, typename T, typename LessThan>
 container_algorithm_internal::ContainerIter<Sequence> c_upper_bound(
-    Sequence& sequence, T&& value, LessThan&& comp) {
+    Sequence& sequence, const T& value, LessThan&& comp) {
   return std::upper_bound(container_algorithm_internal::c_begin(sequence),
-                          container_algorithm_internal::c_end(sequence),
-                          std::forward<T>(value), std::forward<LessThan>(comp));
+                          container_algorithm_internal::c_end(sequence), value,
+                          std::forward<LessThan>(comp));
 }
 
 // c_equal_range()
@@ -1110,20 +1110,19 @@ container_algorithm_internal::ContainerIter<Sequence> c_upper_bound(
 // sorted container which compare equal to `value`.
 template <typename Sequence, typename T>
 container_algorithm_internal::ContainerIterPairType<Sequence, Sequence>
-c_equal_range(Sequence& sequence, T&& value) {
+c_equal_range(Sequence& sequence, const T& value) {
   return std::equal_range(container_algorithm_internal::c_begin(sequence),
-                          container_algorithm_internal::c_end(sequence),
-                          std::forward<T>(value));
+                          container_algorithm_internal::c_end(sequence), value);
 }
 
 // Overload of c_equal_range() for performing a `comp` comparison other than
 // the default `operator<`.
 template <typename Sequence, typename T, typename LessThan>
 container_algorithm_internal::ContainerIterPairType<Sequence, Sequence>
-c_equal_range(Sequence& sequence, T&& value, LessThan&& comp) {
+c_equal_range(Sequence& sequence, const T& value, LessThan&& comp) {
   return std::equal_range(container_algorithm_internal::c_begin(sequence),
-                          container_algorithm_internal::c_end(sequence),
-                          std::forward<T>(value), std::forward<LessThan>(comp));
+                          container_algorithm_internal::c_end(sequence), value,
+                          std::forward<LessThan>(comp));
 }
 
 // c_binary_search()
@@ -1132,20 +1131,19 @@ c_equal_range(Sequence& sequence, T&& value, LessThan&& comp) {
 // to test if any element in the sorted container contains a value equivalent to
 // 'value'.
 template <typename Sequence, typename T>
-bool c_binary_search(Sequence&& sequence, T&& value) {
+bool c_binary_search(Sequence&& sequence, const T& value) {
   return std::binary_search(container_algorithm_internal::c_begin(sequence),
                             container_algorithm_internal::c_end(sequence),
-                            std::forward<T>(value));
+                            value);
 }
 
 // Overload of c_binary_search() for performing a `comp` comparison other than
 // the default `operator<`.
 template <typename Sequence, typename T, typename LessThan>
-bool c_binary_search(Sequence&& sequence, T&& value, LessThan&& comp) {
+bool c_binary_search(Sequence&& sequence, const T& value, LessThan&& comp) {
   return std::binary_search(container_algorithm_internal::c_begin(sequence),
                             container_algorithm_internal::c_end(sequence),
-                            std::forward<T>(value),
-                            std::forward<LessThan>(comp));
+                            value, std::forward<LessThan>(comp));
 }
 
 //------------------------------------------------------------------------------
@@ -1560,8 +1558,8 @@ container_algorithm_internal::ContainerIter<Sequence> c_max_element(
 // smallest and largest values, respectively, using `operator<` to make the
 // comparisons.
 template <typename C>
-container_algorithm_internal::ContainerIterPairType<C, C>
-c_minmax_element(C& c) {
+container_algorithm_internal::ContainerIterPairType<C, C> c_minmax_element(
+    C& c) {
   return std::minmax_element(container_algorithm_internal::c_begin(c),
                              container_algorithm_internal::c_end(c));
 }
@@ -1569,8 +1567,8 @@ c_minmax_element(C& c) {
 // Overload of c_minmax_element() for performing `comp` comparisons other than
 // `operator<`.
 template <typename C, typename LessThan>
-container_algorithm_internal::ContainerIterPairType<C, C>
-c_minmax_element(C& c, LessThan&& comp) {
+container_algorithm_internal::ContainerIterPairType<C, C> c_minmax_element(
+    C& c, LessThan&& comp) {
   return std::minmax_element(container_algorithm_internal::c_begin(c),
                              container_algorithm_internal::c_end(c),
                              std::forward<LessThan>(comp));
@@ -1588,7 +1586,8 @@ c_minmax_element(C& c, LessThan&& comp) {
 // that capital letters ("A-Z") have ASCII values less than lowercase letters
 // ("a-z").
 template <typename Sequence1, typename Sequence2>
-bool c_lexicographical_compare(Sequence1&& sequence1, Sequence2&& sequence2) {
+bool c_lexicographical_compare(const Sequence1& sequence1,
+                               const Sequence2& sequence2) {
   return std::lexicographical_compare(
       container_algorithm_internal::c_begin(sequence1),
       container_algorithm_internal::c_end(sequence1),
@@ -1599,8 +1598,8 @@ bool c_lexicographical_compare(Sequence1&& sequence1, Sequence2&& sequence2) {
 // Overload of c_lexicographical_compare() for performing a lexicographical
 // comparison using a `comp` operator instead of `operator<`.
 template <typename Sequence1, typename Sequence2, typename LessThan>
-bool c_lexicographical_compare(Sequence1&& sequence1, Sequence2&& sequence2,
-                               LessThan&& comp) {
+bool c_lexicographical_compare(const Sequence1& sequence1,
+                               const Sequence2& sequence2, LessThan&& comp) {
   return std::lexicographical_compare(
       container_algorithm_internal::c_begin(sequence1),
       container_algorithm_internal::c_end(sequence1),
@@ -1659,11 +1658,11 @@ bool c_prev_permutation(C& c, LessThan&& comp) {
 // to compute successive values of `value`, as if incremented with `++value`
 // after each element is written. and write them to the container.
 template <typename Sequence, typename T>
-void c_iota(Sequence& sequence, T&& value) {
+void c_iota(Sequence& sequence, const T& value) {
   std::iota(container_algorithm_internal::c_begin(sequence),
-            container_algorithm_internal::c_end(sequence),
-            std::forward<T>(value));
+            container_algorithm_internal::c_end(sequence), value);
 }
+
 // c_accumulate()
 //
 // Container-based version of the <numeric> `std::accumulate()` function