sqlite: add tagged template support

Adding tagged template and LRU cache for prepared
statements in SQLite.

Author: 0hmX

src/lru_cache-inl.h

@@ -0,0 +1,64 @@
+#ifndef SRC_LRU_CACHE_INL_H_
+#define SRC_LRU_CACHE_INL_H_
+
+#include <list>
+#include <unordered_map>
+#include <utility>
+
+template <typename key_t, typename value_t>
+class LruCache {
+ public:
+  using key_value_pair_t = typename std::pair<key_t, value_t>;
+  using iterator = typename std::list<key_value_pair_t>::iterator;
+
+  explicit LruCache(size_t capacity) : capacity_(capacity) {}
+
+  void put(const key_t& key, const value_t& value) {
+    auto it = lookup_map_.find(key);
+    if (it != lookup_map_.end()) {
+      lru_list_.erase(it->second);
+      lookup_map_.erase(it);
+    }
+
+    lru_list_.push_front(std::make_pair(key, value));
+    lookup_map_[key] = lru_list_.begin();
+
+    if (lookup_map_.size() > capacity_) {
+      auto last = lru_list_.end();
+      last--;
+      lookup_map_.erase(last->first);
+      lru_list_.pop_back();
+    }
+  }
+
+  value_t& get(const key_t& key) {
+    auto it = lookup_map_.find(key);
+    lru_list_.splice(lru_list_.begin(), lru_list_,
+                             it->second);
+    return it->second->second;
+  }
+
+  void erase(const key_t& key) {
+    auto it = lookup_map_.find(key);
+    if (it != lookup_map_.end()) {
+      lru_list_.erase(it->second);
+      lookup_map_.erase(it);
+    }
+  }
+
+  bool exists(const key_t& key) const {
+    return lookup_map_.count(key) > 0;
+  }
+
+  size_t size() const {
+    return lookup_map_.size();
+  }
+
+ private:
+  std::list<key_value_pair_t> lru_list_;
+  std::unordered_map<key_t, iterator> lookup_map_;
+  size_t capacity_;
+};
+
+#endif  // SRC_LRU_CACHE_INL_H_
+