Remove std::variant (#23)

Author: improbable-til

phtree/v16/entry.h

@@ -20,10 +20,8 @@
 #include "../../phtree/common/common.h"
 #include "node.h"
 #include <cassert>
-#include <cstdint>
 #include <memory>
-#include <string>
-#include <variant>
+#include <optional>
 
 namespace improbable::phtree::v16 {
 
@@ -44,69 +42,85 @@ class Entry {
     using NodeT = Node<DIM, T, SCALAR>;
 
   public:
-    Entry() : kd_key_(), value_{std::in_place_type<ValueT>, T{}} {}
-
     /*
      * Construct entry with existing node.
      */
-    Entry(const KeyT& k, std::unique_ptr<NodeT>&& node)
-    : kd_key_{k}
-    , value_{
-          std::in_place_type<std::unique_ptr<NodeT>>, std::forward<std::unique_ptr<NodeT>>(node)} {}
+    Entry(const KeyT& k, std::unique_ptr<NodeT>&& node_ptr)
+    : kd_key_{k}, node_{std::move(node_ptr)}, value_{std::nullopt} {}
 
     /*
      * Construct entry with a new node.
      */
     Entry(bit_width_t infix_len, bit_width_t postfix_len)
-    : kd_key_()
-    , value_{
-          std::in_place_type<std::unique_ptr<NodeT>>,
-          std::make_unique<NodeT>(infix_len, postfix_len)} {}
+    : kd_key_(), node_{std::make_unique<NodeT>(infix_len, postfix_len)}, value_{std::nullopt} {}
+
+    /*
+     * Construct entry with existing T.
+     */
+    Entry(const KeyT& k, std::optional<ValueT>&& value)
+    : kd_key_{k}, node_{nullptr}, value_{std::move(value)} {}
 
     /*
      * Construct entry with new T or moved T.
      */
     template <typename... Args>
     explicit Entry(const KeyT& k, Args&&... args)
-    : kd_key_{k}, value_{std::in_place_type<ValueT>, std::forward<Args>(args)...} {}
+    : kd_key_{k}, node_{nullptr}, value_{std::in_place, std::forward<Args>(args)...} {}
 
     [[nodiscard]] const KeyT& GetKey() const {
         return kd_key_;
     }
 
     [[nodiscard]] bool IsValue() const {
-        return std::holds_alternative<ValueT>(value_);
+        return value_.has_value();
     }
 
     [[nodiscard]] bool IsNode() const {
-        return std::holds_alternative<std::unique_ptr<NodeT>>(value_);
+        return node_.get() != nullptr;
     }
 
     [[nodiscard]] T& GetValue() const {
         assert(IsValue());
-        return const_cast<T&>(std::get<ValueT>(value_));
+        return const_cast<T&>(*value_);
     }
 
     [[nodiscard]] NodeT& GetNode() const {
         assert(IsNode());
-        return *std::get<std::unique_ptr<NodeT>>(value_);
+        return *node_;
+    }
+
+    void SetNode(std::unique_ptr<NodeT>&& node) {
+        assert(!IsNode());
+        node_ = std::move(node);
+        value_.reset();
+    }
+
+    [[nodiscard]] std::optional<ValueT>&& ExtractValue() {
+        assert(IsValue());
+        return std::move(value_);
+    }
+
+    [[nodiscard]] std::unique_ptr<NodeT>&& ExtractNode() {
+        assert(IsNode());
+        return std::move(node_);
     }
 
     void ReplaceNodeWithDataFromEntry(Entry&& other) {
         assert(IsNode());
         kd_key_ = other.GetKey();
 
-        // 'value_' points indirectly to 'entry' so we have to remove `entity's` content before
-        // assigning anything to `value_` here. Otherwise the assignment would destruct the previous
-        // content and, by reachability, `entity's` content.
-        auto old_node = std::get<std::unique_ptr<NodeT>>(value_).release();
-        value_ = std::move(other.value_);
-        delete old_node;
+        if (other.IsNode()) {
+            node_ = std::move(other.node_);
+        } else {
+            value_ = std::move(other.value_);
+            node_.reset();
+        }
     }
 
   private:
     KeyT kd_key_;
-    std::variant<ValueT, std::unique_ptr<NodeT>> value_;
+    std::unique_ptr<NodeT> node_;
+    std::optional<ValueT> value_;
 };
 }  // namespace improbable::phtree::v16
 

phtree/v16/node.h

@@ -285,13 +285,15 @@ class Node {
         return entries_.try_emplace(hc_pos, new_key, std::forward<Args>(args)...).first->second;
     }
 
-    void WriteEntry(hc_pos_t hc_pos, EntryT&& entry) {
+    void WriteEntry(hc_pos_t hc_pos, EntryT& entry) {
         if (entry.IsNode()) {
             auto& node = entry.GetNode();
             bit_width_t new_subnode_infix_len = postfix_len_ - node.postfix_len_ - 1;
             node.SetInfixLen(new_subnode_infix_len);
+            entries_.try_emplace(hc_pos, entry.GetKey(), entry.ExtractNode());
+        } else {
+            entries_.try_emplace(hc_pos, entry.GetKey(), entry.ExtractValue());
         }
-        entries_.try_emplace(hc_pos, std::move(entry));
     }
 
     /*
@@ -356,13 +358,11 @@ class Node {
         hc_pos_t pos_sub_2 = CalcPosInArray(current_key, new_postfix_len);
 
         // Move key/value into subnode
-        new_sub_node->WriteEntry(pos_sub_2, std::move(current_entry));
+        new_sub_node->WriteEntry(pos_sub_2, current_entry);
         auto& new_entry = new_sub_node->WriteValue(pos_sub_1, new_key, std::forward<Args>(args)...);
 
         // Insert new node into local node
-        // We use new_key because current_key has been moved().
-        // TODO avoid reassigning the key here, this is unnecessary.
-        current_entry = {new_key, std::move(new_sub_node)};
+        current_entry.SetNode(std::move(new_sub_node));
         return &new_entry;
     }