In b-tree, support unassignable value types.

Avoid using value move/swap and delete those functions from slot_policy types. There was only one use of params_type::move in `erase`.

PiperOrigin-RevId: 453237739
Change-Id: Ie81c6dba6c4db34e97a067d2c0defcded8044a5a

absl/container/btree_set.h

@@ -766,17 +766,6 @@ struct set_slot_policy {
     construct(alloc, new_slot, old_slot);
     destroy(alloc, old_slot);
   }
-
-  template <typename Alloc>
-  static void swap(Alloc * /*alloc*/, slot_type *a, slot_type *b) {
-    using std::swap;
-    swap(*a, *b);
-  }
-
-  template <typename Alloc>
-  static void move(Alloc * /*alloc*/, slot_type *src, slot_type *dest) {
-    *dest = std::move(*src);
-  }
 };
 
 // A parameters structure for holding the type parameters for a btree_set.

absl/container/btree_test.cc

@@ -3188,6 +3188,66 @@ TEST(Btree, OnlyConstructibleByAllocatorType) {
   }
 }
 
+class NotAssignable {
+ public:
+  explicit NotAssignable(int i) : i_(i) {}
+  NotAssignable(const NotAssignable &other) : i_(other.i_) {}
+  NotAssignable &operator=(NotAssignable &&other) = delete;
+  int Get() const { return i_; }
+  bool operator==(int i) const { return i_ == i; }
+  friend bool operator<(NotAssignable a, NotAssignable b) {
+    return a.i_ < b.i_;
+  }
+
+ private:
+  int i_;
+};
+
+TEST(Btree, NotAssignableType) {
+  {
+    absl::btree_set<NotAssignable> set;
+    set.emplace(1);
+    set.emplace_hint(set.end(), 2);
+    set.insert(NotAssignable(3));
+    set.insert(set.end(), NotAssignable(4));
+    EXPECT_THAT(set, ElementsAre(1, 2, 3, 4));
+    set.erase(set.begin());
+    EXPECT_THAT(set, ElementsAre(2, 3, 4));
+  }
+  {
+    absl::btree_multiset<NotAssignable> set;
+    set.emplace(1);
+    set.emplace_hint(set.end(), 2);
+    set.insert(NotAssignable(2));
+    set.insert(set.end(), NotAssignable(3));
+    EXPECT_THAT(set, ElementsAre(1, 2, 2, 3));
+    set.erase(set.begin());
+    EXPECT_THAT(set, ElementsAre(2, 2, 3));
+  }
+  {
+    absl::btree_map<NotAssignable, int> map;
+    map.emplace(NotAssignable(1), 1);
+    map.emplace_hint(map.end(), NotAssignable(2), 2);
+    map.insert({NotAssignable(3), 3});
+    map.insert(map.end(), {NotAssignable(4), 4});
+    EXPECT_THAT(map,
+                ElementsAre(Pair(1, 1), Pair(2, 2), Pair(3, 3), Pair(4, 4)));
+    map.erase(map.begin());
+    EXPECT_THAT(map, ElementsAre(Pair(2, 2), Pair(3, 3), Pair(4, 4)));
+  }
+  {
+    absl::btree_multimap<NotAssignable, int> map;
+    map.emplace(NotAssignable(1), 1);
+    map.emplace_hint(map.end(), NotAssignable(2), 2);
+    map.insert({NotAssignable(2), 3});
+    map.insert(map.end(), {NotAssignable(3), 3});
+    EXPECT_THAT(map,
+                ElementsAre(Pair(1, 1), Pair(2, 2), Pair(2, 3), Pair(3, 3)));
+    map.erase(map.begin());
+    EXPECT_THAT(map, ElementsAre(Pair(2, 2), Pair(2, 3), Pair(3, 3)));
+  }
+}
+
 }  // namespace
 }  // namespace container_internal
 ABSL_NAMESPACE_END

absl/container/internal/btree.h

@@ -462,12 +462,6 @@ struct common_params {
   static void transfer(Alloc *alloc, slot_type *new_slot, slot_type *old_slot) {
     slot_policy::transfer(alloc, new_slot, old_slot);
   }
-  static void swap(Alloc *alloc, slot_type *a, slot_type *b) {
-    slot_policy::swap(alloc, a, b);
-  }
-  static void move(Alloc *alloc, slot_type *src, slot_type *dest) {
-    slot_policy::move(alloc, src, dest);
-  }
 };
 
 // An adapter class that converts a lower-bound compare into an upper-bound
@@ -2300,23 +2294,29 @@ auto btree<P>::operator=(btree &&other) noexcept -> btree & {
 
 template <typename P>
 auto btree<P>::erase(iterator iter) -> iterator {
-  bool internal_delete = false;
-  if (iter.node_->is_internal()) {
-    // Deletion of a value on an internal node. First, move the largest value
-    // from our left child here, then delete that position (in remove_values()
-    // below). We can get to the largest value from our left child by
-    // decrementing iter.
+  iter.node_->value_destroy(iter.position_, mutable_allocator());
+  iter.update_generation();
+
+  const bool internal_delete = iter.node_->is_internal();
+  if (internal_delete) {
+    // Deletion of a value on an internal node. First, transfer the largest
+    // value from our left child here, then erase/rebalance from that position.
+    // We can get to the largest value from our left child by decrementing iter.
     iterator internal_iter(iter);
     --iter;
     assert(iter.node_->is_leaf());
-    params_type::move(mutable_allocator(), iter.node_->slot(iter.position_),
-                      internal_iter.node_->slot(internal_iter.position_));
-    internal_delete = true;
-  }
-
-  // Delete the key from the leaf.
-  iter.node_->remove_values(iter.position_, /*to_erase=*/1,
-                            mutable_allocator());
+    internal_iter.node_->transfer(internal_iter.position_, iter.position_,
+                                  iter.node_, mutable_allocator());
+  } else {
+    // Shift values after erased position in leaf. In the internal case, we
+    // don't need to do this because the leaf position is the end of the node.
+    const field_type transfer_from = iter.position_ + 1;
+    const field_type num_to_transfer = iter.node_->finish() - transfer_from;
+    iter.node_->transfer_n(num_to_transfer, iter.position_, transfer_from,
+                           iter.node_, mutable_allocator());
+  }
+  // Update node finish and container size.
+  iter.node_->set_finish(iter.node_->finish() - 1);
   --size_;
 
   // We want to return the next value after the one we just erased. If we

absl/container/internal/container_memory.h

@@ -433,33 +433,6 @@ struct map_slot_policy {
     }
     destroy(alloc, old_slot);
   }
-
-  template <class Allocator>
-  static void swap(Allocator* alloc, slot_type* a, slot_type* b) {
-    if (kMutableKeys::value) {
-      using std::swap;
-      swap(a->mutable_value, b->mutable_value);
-    } else {
-      value_type tmp = std::move(a->value);
-      absl::allocator_traits<Allocator>::destroy(*alloc, &a->value);
-      absl::allocator_traits<Allocator>::construct(*alloc, &a->value,
-                                                   std::move(b->value));
-      absl::allocator_traits<Allocator>::destroy(*alloc, &b->value);
-      absl::allocator_traits<Allocator>::construct(*alloc, &b->value,
-                                                   std::move(tmp));
-    }
-  }
-
-  template <class Allocator>
-  static void move(Allocator* alloc, slot_type* src, slot_type* dest) {
-    if (kMutableKeys::value) {
-      dest->mutable_value = std::move(src->mutable_value);
-    } else {
-      absl::allocator_traits<Allocator>::destroy(*alloc, &dest->value);
-      absl::allocator_traits<Allocator>::construct(*alloc, &dest->value,
-                                                   std::move(src->value));
-    }
-  }
 };
 
 }  // namespace container_internal