diff --git a/source/mijin/container/vector_map.hpp b/source/mijin/container/vector_map.hpp
index 0c3e6ef..a675e48 100644
--- a/source/mijin/container/vector_map.hpp
+++ b/source/mijin/container/vector_map.hpp
@@ -4,6 +4,7 @@
 #if !defined(MIJIN_CONTAINER_VECTOR_MAP_HPP_INCLUDED)
 #define MIJIN_CONTAINER_VECTOR_MAP_HPP_INCLUDED 1
 
+#include <algorithm>
 #include <stdexcept>
 #include <vector>
 #include "./boxed_object.hpp"
@@ -140,6 +141,16 @@ public:
     {
         return at(key);
     }
+
+    TValue& operator[](TKey&& key)
+    {
+        auto it = find(key);
+        if (it != end())
+        {
+            return it->second;
+        }
+        return emplace(std::move(key), TValue()).first->second;
+    }
     
     [[nodiscard]]
     iterator begin() MIJIN_NOEXCEPT { return {keys_.data(), values_.data()}; }
@@ -234,6 +245,7 @@ public:
         return eraseImpl(idx, count);
     }
 
+    [[nodiscard]]
     iterator find(const TKey& key) MIJIN_NOEXCEPT
     {
         for (std::size_t idx = 0; idx < keys_.size(); ++idx)
@@ -246,6 +258,7 @@ public:
         return end();
     }
 
+    [[nodiscard]]
     const_iterator find(const TKey& key) const MIJIN_NOEXCEPT
     {
         for (std::size_t idx = 0; idx < keys_.size(); ++idx)
@@ -257,6 +270,12 @@ public:
         }
         return end();
     }
+
+    [[nodiscard]]
+    bool contains(const TKey& key) const MIJIN_NOEXCEPT
+    {
+        return std::ranges::contains(keys_, key);
+    }
 private:
     iterator eraseImpl(std::ptrdiff_t idx, std::ptrdiff_t count = 1) MIJIN_NOEXCEPT
     {