diff --git a/include/libconcur/data_model.h b/include/libconcur/data_model.h
index 514b26d..e6865d4 100644
--- a/include/libconcur/data_model.h
+++ b/include/libconcur/data_model.h
@@ -11,7 +11,7 @@
 #include <cstddef>
 #include <cstdint>
 
-#include "libimp/construct.h"
+#include "libimp/uninitialized.h"
 #include "libimp/detect_plat.h"
 #include "libimp/aligned.h"
 
diff --git a/include/libimp/expected.h b/include/libimp/expected.h
index 533e355..af2ee7d 100644
--- a/include/libimp/expected.h
+++ b/include/libimp/expected.h
@@ -13,7 +13,7 @@
 #include <cstddef>  // std::nullptr_t
 
 #include "libimp/def.h"
-#include "libimp/construct.h"
+#include "libimp/uninitialized.h"
 #include "libimp/generic.h"
 #include "libimp/byte.h"
 
diff --git a/include/libimp/generic.h b/include/libimp/generic.h
index e030181..2106adc 100644
--- a/include/libimp/generic.h
+++ b/include/libimp/generic.h
@@ -21,6 +21,12 @@ LIBIMP_NAMESPACE_BEG_
 template <typename...>
 using void_t = void;
 
+/**
+ * \brief A type-list for generic programming.
+*/
+template <typename...>
+struct types {};
+
 /**
  * \brief To indicate that the contained object should be constructed in-place.
  * \see https://en.cppreference.com/w/cpp/utility/in_place
diff --git a/include/libimp/pimpl.h b/include/libimp/pimpl.h
index df7787a..d0b0b2b 100644
--- a/include/libimp/pimpl.h
+++ b/include/libimp/pimpl.h
@@ -10,7 +10,7 @@
 #include <type_traits>
 #include <cstdint>
 
-#include "libimp/construct.h"
+#include "libimp/uninitialized.h"
 #include "libimp/def.h"
 
 LIBIMP_NAMESPACE_BEG_
diff --git a/include/libimp/construct.h b/include/libimp/uninitialized.h
similarity index 58%
rename from include/libimp/construct.h
rename to include/libimp/uninitialized.h
index 851c657..335d001 100644
--- a/include/libimp/construct.h
+++ b/include/libimp/uninitialized.h
@@ -1,7 +1,7 @@
 /**
- * \file libimp/construct.h
+ * \file libimp/uninitialized.h
  * \author mutouyun (orz@orzz.org)
- * \brief Construct an object from a memory buffer
+ * \brief Uninitialized memory algorithms.
  * \date 2022-02-27
  */
 #pragma once
@@ -14,6 +14,7 @@
 
 #include "libimp/def.h"
 #include "libimp/detect_plat.h"
+#include "libimp/horrible_cast.h"
 
 LIBIMP_NAMESPACE_BEG_
 
@@ -67,4 +68,42 @@ void *destroy(T (*p)[N]) noexcept {
   return p;
 }
 
+/**
+ * \brief Destroys a range of objects.
+ * \see https://en.cppreference.com/w/cpp/memory/destroy
+*/
+template <typename ForwardIt>
+void destroy(ForwardIt first, ForwardIt last) noexcept {
+#if defined(LIBIMP_CPP_17)
+  std::destroy(first, last);
+#else
+  for (; first != last; ++first) {
+    destroy(std::addressof(*first));
+  }
+#endif
+}
+
+/**
+ * \brief Constructs objects by default-initialization 
+ * in an uninitialized area of memory, defined by a start and a count.
+ * \see https://en.cppreference.com/w/cpp/memory/uninitialized_default_construct_n
+*/
+template <typename ForwardIt, typename Size>
+ForwardIt uninitialized_default_construct_n(ForwardIt first, Size n) {
+#if defined(LIBIMP_CPP_17)
+  return std::uninitialized_default_construct_n(first, n);
+#else
+  using T = typename std::iterator_traits<ForwardIt>::value_type;
+  ForwardIt current = first;
+  LIBIMP_TRY {
+    for (; n > 0; (void) ++current, --n)
+      ::new (horrible_cast<void *>(std::addressof(*current))) T;
+    return current;
+  } LIBIMP_CATCH(...) {
+    destroy(first, current);
+    LIBIMP_THROW(, first);
+  }
+#endif
+}
+
 LIBIMP_NAMESPACE_END_
diff --git a/include/libpmr/allocator.h b/include/libpmr/allocator.h
index 9acaeae..f12eca2 100644
--- a/include/libpmr/allocator.h
+++ b/include/libpmr/allocator.h
@@ -10,7 +10,7 @@
 #include <array>
 
 #include "libimp/export.h"
-#include "libimp/construct.h"
+#include "libimp/uninitialized.h"
 #include "libimp/byte.h"
 
 #include "libpmr/def.h"
diff --git a/include/libpmr/small_storage.h b/include/libpmr/small_storage.h
index eb830ec..79c613c 100644
--- a/include/libpmr/small_storage.h
+++ b/include/libpmr/small_storage.h
@@ -14,28 +14,33 @@
 #include <cstddef>
 
 #include "libimp/export.h"
-#include "libimp/construct.h"
+#include "libimp/uninitialized.h"
 #include "libimp/byte.h"
 #include "libimp/generic.h"
 
 #include "libpmr/def.h"
+#include "libpmr/allocator.h"
 
 LIBPMR_NAMESPACE_BEG_
 
-class LIBIMP_EXPORT allocator;
-
 /**
  * \class holder_base
  * \brief Data holder base class.
 */
 class holder_base {
+
+  // non-copyable
+  holder_base(holder_base const &) = delete;
+  holder_base &operator=(holder_base const &) = delete;
+
 public:
+  holder_base() noexcept = default;
   virtual ~holder_base() noexcept = default;
   virtual bool valid() const noexcept = 0;
   virtual std::type_info const &type() const noexcept = 0;
   virtual std::size_t sizeof_type() const noexcept = 0;
+  virtual std::size_t sizeof_heap() const noexcept = 0;
   virtual std::size_t count() const noexcept = 0;
-  virtual std::size_t size () const noexcept = 0;
   virtual void *get() noexcept = 0;
   virtual void const *get() const noexcept = 0;
 
@@ -55,8 +60,8 @@ public:
   bool valid() const noexcept override { return false; }
   std::type_info const &type() const noexcept override { return typeid(nullptr);}
   std::size_t sizeof_type() const noexcept override { return 0; }
+  std::size_t sizeof_heap() const noexcept override { return 0; }
   std::size_t count() const noexcept override { return 0; }
-  std::size_t size () const noexcept override { return 0; }
   void *get() noexcept override { return nullptr; }
   void const *get() const noexcept override { return nullptr; }
   void move_to(allocator const &, void *) noexcept override {}
@@ -81,7 +86,7 @@ public:
   holder() = default; // uninitialized
 
   template <typename... A>
-  holder(::LIBIMP::in_place_t, A &&...args) {
+  holder(allocator const &, A &&...args) {
     ::LIBIMP::construct<Value>(value_storage_.data(), std::forward<A>(args)...);
   }
 
@@ -97,12 +102,12 @@ public:
     return sizeof(Value);
   }
 
-  std::size_t count() const noexcept override {
-    return 1;
+  std::size_t sizeof_heap() const noexcept override {
+    return 0;
   }
 
-  std::size_t size() const noexcept override {
-    return value_storage_.size();
+  std::size_t count() const noexcept override {
+    return 1;
   }
 
   void *get() noexcept override {
@@ -113,16 +118,16 @@ public:
     return value_storage_.data();
   }
 
-  void move_to(allocator const &, void *p) noexcept override {
-    ::LIBIMP::construct<holder>(p, ::LIBIMP::in_place, std::move(*static_cast<Value *>(get())));
+  void move_to(allocator const &alloc, void *p) noexcept override {
+    ::LIBIMP::construct<holder>(p, alloc, std::move(*static_cast<Value *>(get())));
   }
 
-  void copy_to(allocator const &, void *p) const noexcept(false) override {
-    ::LIBIMP::construct<holder>(p, ::LIBIMP::in_place, *static_cast<Value *>(get()));
+  void copy_to(allocator const &alloc, void *p) const noexcept(false) override {
+    ::LIBIMP::construct<holder>(p, alloc, *static_cast<Value const *>(get()));
   }
 
   void destroy(allocator const &) noexcept override {
-    ::LIBIMP::destroy<Value>(value_storage_.data());
+    ::LIBIMP::destroy(static_cast<Value *>(get()));
   }
 };
 
@@ -134,10 +139,177 @@ public:
 template <typename Value>
 class holder<Value, false> : public holder_base {
 
-  Value *value_ptr_ = nullptr;
+  Value *value_ptr_;
 
 public:
-  holder() = default; // uninitialized
+  holder() noexcept : value_ptr_(nullptr) {}
+
+  template <typename... A>
+  holder(allocator const &alloc, A &&...args) {
+    void *p = alloc.allocate(sizeof(Value), alignof(Value));
+    if (p == nullptr) return;
+    value_ptr_ = ::LIBIMP::construct<Value>(p, std::forward<A>(args)...);
+  }
+
+  bool valid() const noexcept override {
+    return value_ptr_ != nullptr;
+  }
+
+  std::type_info const &type() const noexcept override {
+    return typeid(Value);
+  }
+
+  std::size_t sizeof_type() const noexcept override {
+    return sizeof(Value);
+  }
+
+  std::size_t sizeof_heap() const noexcept override {
+    return sizeof(Value);
+  }
+
+  std::size_t count() const noexcept override {
+    return 1;
+  }
+
+  void *get() noexcept override {
+    return value_ptr_;
+  }
+
+  void const *get() const noexcept override {
+    return value_ptr_;
+  }
+
+  void move_to(allocator const &alloc, void *p) noexcept override {
+    if (value_ptr_ == nullptr) {
+      ::LIBIMP::construct<holder>(p);
+      return;
+    }
+    ::LIBIMP::construct<holder>(p, alloc, std::move(*value_ptr_));
+  }
+
+  void copy_to(allocator const &alloc, void *p) const noexcept(false) override {
+    if (value_ptr_ == nullptr) {
+      ::LIBIMP::construct<holder>(p);
+      return;
+    }
+    ::LIBIMP::construct<holder>(p, alloc, *value_ptr_);
+  }
+
+  void destroy(allocator const &alloc) noexcept override {
+    alloc.deallocate(::LIBIMP::destroy(value_ptr_), sizeof(Value), alignof(Value));
+  }
+};
+
+namespace detail {
+
+struct holder_info {
+  std::type_info const *type;
+  std::size_t sizeof_type;
+  std::size_t count;
+  void (*copy)(allocator const &, void const *s, void *d);
+};
+
+template <typename Value, typename Construct>
+void *holder_construct(allocator const &alloc, std::size_t n, Construct &&c) {
+  void *p = alloc.allocate(n * sizeof(Value));
+  if (p == nullptr) return nullptr;
+  LIBIMP_TRY {
+    std::forward<Construct>(c)(static_cast<Value *>(p), n);
+    return p;
+  } LIBIMP_CATCH(...) {
+    alloc.deallocate(p, n * sizeof(Value));
+    LIBIMP_THROW(, nullptr);
+  }
+}
+
+} // namespace detail
+
+/**
+ * \class template <> holder<void, true>
+ * \brief A holder implementation of some data objects that stores type information on stack memory.
+ */
+template <>
+class holder<void, true> : public holder_base {
+
+  detail::holder_info info_;
+  void *value_ptr_;
+
+public:
+  holder() noexcept
+    : info_{&typeid(nullptr)}
+    , value_ptr_(nullptr) {}
+
+  /// \brief Constructs a holder with type of `Value`.
+  /// alignof(Value) must be less than or equal to alignof(std::max_align_t).
+  template <typename Value, 
+            std::enable_if_t<alignof(Value) <= alignof(std::max_align_t), bool> = true>
+  holder(allocator const &alloc, ::LIBIMP::types<Value>, std::size_t n) : holder() {
+    value_ptr_ = detail::holder_construct<Value>(alloc, n, 
+      ::LIBIMP::uninitialized_default_construct_n<Value *, std::size_t>);
+    if (value_ptr_ == nullptr) return;
+    info_.type = &typeid(Value);
+    info_.sizeof_type = sizeof(Value);
+    info_.count = n;
+    info_.copy = [](allocator const &alloc, void const *s, void *d) {
+      auto const &src = *static_cast<holder const *>(s);
+      auto &      dst = *::LIBIMP::construct<holder>(d);
+      if (!src.valid()) return;
+      dst.value_ptr_ = detail::holder_construct<Value>(alloc, src.count(), [s = src.get()](Value *d, std::size_t n) {
+        std::uninitialized_copy_n(static_cast<Value const *>(s), n, d);
+      });
+      if (dst.value_ptr_ == nullptr) return;
+      dst.info_ = src.info_;
+    };
+  }
+
+  bool valid() const noexcept override {
+    return value_ptr_ != nullptr;
+  }
+
+  std::type_info const &type() const noexcept override {
+    return *info_.type;
+  }
+
+  std::size_t sizeof_type() const noexcept override {
+    return info_.sizeof_type;
+  }
+
+  std::size_t sizeof_heap() const noexcept override {
+    return info_.sizeof_type * info_.count;
+  }
+
+  std::size_t count() const noexcept override {
+    return info_.count;
+  }
+
+  void *get() noexcept override {
+    return value_ptr_;
+  }
+
+  void const *get() const noexcept override {
+    return value_ptr_;
+  }
+
+  void move_to(allocator const &, void *p) noexcept override {
+    auto *des = ::LIBIMP::construct<holder>(p);
+    if (value_ptr_ == nullptr) {
+      return;
+    }
+    std::swap(value_ptr_, des->value_ptr_);
+    std::swap(info_, des->info_);
+  }
+
+  void copy_to(allocator const &alloc, void *p) const noexcept(false) override {
+    auto *des = ::LIBIMP::construct<holder>(p);
+    if (value_ptr_ == nullptr) {
+      return;
+    }
+    info_.copy(alloc, this, des);
+  }
+
+  void destroy(allocator const &alloc) noexcept override {
+    alloc.deallocate(::LIBIMP::destroy(value_ptr_), info_.sizeof_type * info_.count);
+  }
 };
 
 LIBPMR_NAMESPACE_END_
diff --git a/test/imp/test_imp_utility.cpp b/test/imp/test_imp_utility.cpp
index 1de8bb4..3c6ba5d 100644
--- a/test/imp/test_imp_utility.cpp
+++ b/test/imp/test_imp_utility.cpp
@@ -5,7 +5,7 @@
 
 #include "gtest/gtest.h"
 
-#include "libimp/construct.h"
+#include "libimp/uninitialized.h"
 #include "libimp/pimpl.h"
 #include "libimp/countof.h"
 #include "libimp/dataof.h"
diff --git a/test/pmr/test_pmr_small_storage.cpp b/test/pmr/test_pmr_small_storage.cpp
index e3629a3..6b5e1d9 100644
--- a/test/pmr/test_pmr_small_storage.cpp
+++ b/test/pmr/test_pmr_small_storage.cpp
@@ -1,7 +1,86 @@
 
+#include <type_traits>
+#include <utility>
+
 #include "gtest/gtest.h"
 
 #include "libpmr/small_storage.h"
 
+TEST(small_storage, holder_construct) {
+  pmr::holder_null();
+  pmr::holder<int, true>();
+  pmr::holder<int, false>();
+  pmr::holder<void, true>();
+  SUCCEED();
+}
+
+TEST(small_storage, holder_copy_move_construct) {
+  EXPECT_FALSE(std::is_copy_constructible<pmr::holder_null>::value);
+  EXPECT_FALSE((std::is_copy_constructible<pmr::holder<int, true>>::value));
+  EXPECT_FALSE((std::is_copy_constructible<pmr::holder<int, false>>::value));
+  EXPECT_FALSE((std::is_copy_constructible<pmr::holder<void, true>>::value));
+
+  EXPECT_FALSE(std::is_copy_assignable<pmr::holder_null>::value);
+  EXPECT_FALSE((std::is_copy_assignable<pmr::holder<int, true>>::value));
+  EXPECT_FALSE((std::is_copy_assignable<pmr::holder<int, false>>::value));
+  EXPECT_FALSE((std::is_copy_assignable<pmr::holder<void, true>>::value));
+
+  EXPECT_FALSE(std::is_move_constructible<pmr::holder_null>::value);
+  EXPECT_FALSE((std::is_move_constructible<pmr::holder<int, true>>::value));
+  EXPECT_FALSE((std::is_move_constructible<pmr::holder<int, false>>::value));
+  EXPECT_FALSE((std::is_move_constructible<pmr::holder<void, true>>::value));
+
+  EXPECT_FALSE(std::is_move_assignable<pmr::holder_null>::value);
+  EXPECT_FALSE((std::is_move_assignable<pmr::holder<int, true>>::value));
+  EXPECT_FALSE((std::is_move_assignable<pmr::holder<int, false>>::value));
+  EXPECT_FALSE((std::is_move_assignable<pmr::holder<void, true>>::value));
+}
+
+TEST(small_storage, holder_copy_move) {
+  struct foo {
+    int i;
+    foo(int i) : i(i) {}
+    foo(foo const &rhs) : i(rhs.i) {}
+    foo(foo &&rhs) : i(std::exchange(rhs.i, 0)) {}
+  };
+
+  pmr::allocator alc;
+  pmr::holder<foo, true> h1(alc, 1);
+  pmr::holder<foo, true> h2, h3; // uninitialized
+  h1.copy_to(alc, &h2);
+  EXPECT_EQ(static_cast<foo *>(h1.get())->i, 1);
+  EXPECT_EQ(static_cast<foo *>(h2.get())->i, 1);
+  h1.move_to(alc, &h3);
+  EXPECT_EQ(static_cast<foo *>(h1.get())->i, 0);
+  EXPECT_EQ(static_cast<foo *>(h3.get())->i, 1);
+  h1.destroy(alc);
+  h2.destroy(alc);
+  h3.destroy(alc);
+
+  pmr::holder<foo, false> h4(alc, 1);
+  pmr::holder<foo, false> h5, h6; // uninitialized
+  h4.copy_to(alc, &h5);
+  EXPECT_EQ(static_cast<foo *>(h4.get())->i, 1);
+  EXPECT_EQ(static_cast<foo *>(h5.get())->i, 1);
+  h4.move_to(alc, &h6);
+  EXPECT_EQ(static_cast<foo *>(h4.get())->i, 0);
+  EXPECT_EQ(static_cast<foo *>(h6.get())->i, 1);
+  h4.destroy(alc);
+  h5.destroy(alc);
+  h6.destroy(alc);
+
+  pmr::holder<void, true> h7(alc, ::LIBIMP::types<int>{}, 10);
+  pmr::holder<void, true> h8, h9; // uninitialized
+  h7.copy_to(alc, &h8);
+  EXPECT_EQ(h7.count(), 10);
+  EXPECT_EQ(h8.count(), 10);
+  h7.move_to(alc, &h9);
+  EXPECT_EQ(h7.count(), 0);
+  EXPECT_EQ(h9.count(), 10);
+  h7.destroy(alc);
+  h8.destroy(alc);
+  h9.destroy(alc);
+}
+
 TEST(small_storage, construct) {
 }