diff --git a/CMakeLists.txt b/CMakeLists.txt
index aa9634eee..d0f8f7e0b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -133,7 +133,7 @@ set(PYBIND11_HEADERS
     include/pybind11/detail/dynamic_raw_ptr_cast_if_possible.h
     include/pybind11/detail/init.h
     include/pybind11/detail/internals.h
-    include/pybind11/detail/smart_holder_poc.h
+    include/pybind11/detail/struct_smart_holder.h
     include/pybind11/detail/type_caster_base.h
     include/pybind11/detail/typeid.h
     include/pybind11/detail/using_smart_holder.h
diff --git a/include/pybind11/detail/smart_holder_poc.h b/include/pybind11/detail/struct_smart_holder.h
similarity index 85%
rename from include/pybind11/detail/smart_holder_poc.h
rename to include/pybind11/detail/struct_smart_holder.h
index 89742ab27..6fdd95f4d 100644
--- a/include/pybind11/detail/smart_holder_poc.h
+++ b/include/pybind11/detail/struct_smart_holder.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2020-2021 The Pybind Development Team.
+// Copyright (c) 2020-2024 The Pybind Development Team.
 // All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
@@ -44,16 +44,6 @@ Details:
 * The `void_cast_raw_ptr` option is needed to make the `smart_holder` `vptr`
   member invisible to the `shared_from_this` mechanism, in case the lifetime
   of a `PyObject` is tied to the pointee.
-
-* Regarding `PYBIND11_TESTS_PURE_CPP_SMART_HOLDER_POC_TEST_CPP` below:
-  This define serves as a marker for code that is NOT used
-  from smart_holder_type_casters.h, but is exercised only from
-  tests/pure_cpp/smart_holder_poc_test.cpp. The marked code was useful
-  mainly for bootstrapping the smart_holder work. At this stage, with
-  smart_holder_type_casters.h in production use (at Google) since around
-  February 2021, it could be moved from here to tests/pure_cpp/ (help welcome).
-  It will probably be best in most cases to add tests for new functionality
-  under test/test_class_sh_*.
 */
 
 #pragma once
@@ -256,26 +246,6 @@ struct smart_holder {
         return static_cast<T *>(vptr.get());
     }
 
-#ifdef PYBIND11_TESTS_PURE_CPP_SMART_HOLDER_POC_TEST_CPP // See comment near top.
-    template <typename T>
-    T &as_lvalue_ref() const {
-        static const char *context = "as_lvalue_ref";
-        ensure_is_populated(context);
-        ensure_has_pointee(context);
-        return *as_raw_ptr_unowned<T>();
-    }
-#endif
-
-#ifdef PYBIND11_TESTS_PURE_CPP_SMART_HOLDER_POC_TEST_CPP // See comment near top.
-    template <typename T>
-    T &&as_rvalue_ref() const {
-        static const char *context = "as_rvalue_ref";
-        ensure_is_populated(context);
-        ensure_has_pointee(context);
-        return std::move(*as_raw_ptr_unowned<T>());
-    }
-#endif
-
     template <typename T>
     static smart_holder from_raw_ptr_take_ownership(T *raw_ptr, bool void_cast_raw_ptr = false) {
         ensure_pointee_is_destructible<T>("from_raw_ptr_take_ownership");
@@ -319,16 +289,6 @@ struct smart_holder {
         release_disowned();
     }
 
-#ifdef PYBIND11_TESTS_PURE_CPP_SMART_HOLDER_POC_TEST_CPP // See comment near top.
-    template <typename T>
-    T *as_raw_ptr_release_ownership(const char *context = "as_raw_ptr_release_ownership") {
-        ensure_can_release_ownership(context);
-        T *raw_ptr = as_raw_ptr_unowned<T>();
-        release_ownership();
-        return raw_ptr;
-    }
-#endif
-
     template <typename T, typename D>
     static smart_holder from_unique_ptr(std::unique_ptr<T, D> &&unq_ptr,
                                         void *void_ptr = nullptr) {
@@ -351,19 +311,6 @@ struct smart_holder {
         return hld;
     }
 
-#ifdef PYBIND11_TESTS_PURE_CPP_SMART_HOLDER_POC_TEST_CPP // See comment near top.
-    template <typename T, typename D = std::default_delete<T>>
-    std::unique_ptr<T, D> as_unique_ptr() {
-        static const char *context = "as_unique_ptr";
-        ensure_compatible_rtti_uqp_del<T, D>(context);
-        ensure_use_count_1(context);
-        T *raw_ptr = as_raw_ptr_unowned<T>();
-        release_ownership();
-        // KNOWN DEFECT (see PR #4850): Does not copy the deleter.
-        return std::unique_ptr<T, D>(raw_ptr);
-    }
-#endif
-
     template <typename T>
     static smart_holder from_shared_ptr(std::shared_ptr<T> shd_ptr) {
         smart_holder hld;
diff --git a/include/pybind11/detail/type_caster_base.h b/include/pybind11/detail/type_caster_base.h
index 92415718f..cc62cfa8e 100644
--- a/include/pybind11/detail/type_caster_base.h
+++ b/include/pybind11/detail/type_caster_base.h
@@ -789,7 +789,7 @@ struct load_helper : value_and_holder_helper {
 
         auto *gd = std::get_deleter<pybindit::memory::guarded_delete>(holder().vptr);
         if (gd && gd->use_del_fun) { // Note the ensure_compatible_rtti_uqp_del<T, D>() call above.
-            // In smart_holder_poc, a custom  deleter is always stored in a guarded delete.
+            // In struct_smart_holder, a custom  deleter is always stored in a guarded delete.
             // The guarded delete's std::function<void(void*)> actually points at the
             // custom_deleter type, so we can verify it is of the custom deleter type and
             // finally extract its deleter.
diff --git a/include/pybind11/detail/using_smart_holder.h b/include/pybind11/detail/using_smart_holder.h
index 3d0463209..826e6b2c6 100644
--- a/include/pybind11/detail/using_smart_holder.h
+++ b/include/pybind11/detail/using_smart_holder.h
@@ -10,7 +10,7 @@
 #include <type_traits>
 
 #ifdef PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
-#    include "smart_holder_poc.h"
+#    include "struct_smart_holder.h"
 #endif
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
diff --git a/tests/extra_python_package/test_files.py b/tests/extra_python_package/test_files.py
index e6602ad79..27c6f6421 100644
--- a/tests/extra_python_package/test_files.py
+++ b/tests/extra_python_package/test_files.py
@@ -58,7 +58,7 @@ detail_headers = {
     "include/pybind11/detail/dynamic_raw_ptr_cast_if_possible.h",
     "include/pybind11/detail/init.h",
     "include/pybind11/detail/internals.h",
-    "include/pybind11/detail/smart_holder_poc.h",
+    "include/pybind11/detail/struct_smart_holder.h",
     "include/pybind11/detail/type_caster_base.h",
     "include/pybind11/detail/typeid.h",
     "include/pybind11/detail/using_smart_holder.h",
diff --git a/tests/pure_cpp/smart_holder_poc.h b/tests/pure_cpp/smart_holder_poc.h
new file mode 100644
index 000000000..320311b7d
--- /dev/null
+++ b/tests/pure_cpp/smart_holder_poc.h
@@ -0,0 +1,51 @@
+// Copyright (c) 2020-2024 The Pybind Development Team.
+// All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#pragma once
+
+#include "pybind11/detail/struct_smart_holder.h"
+
+namespace pybindit {
+namespace memory {
+namespace smart_holder_poc { // Proof-of-Concept implementations.
+
+template <typename T>
+T &as_lvalue_ref(const smart_holder &hld) {
+    static const char *context = "as_lvalue_ref";
+    hld.ensure_is_populated(context);
+    hld.ensure_has_pointee(context);
+    return *hld.as_raw_ptr_unowned<T>();
+}
+
+template <typename T>
+T &&as_rvalue_ref(const smart_holder &hld) {
+    static const char *context = "as_rvalue_ref";
+    hld.ensure_is_populated(context);
+    hld.ensure_has_pointee(context);
+    return std::move(*hld.as_raw_ptr_unowned<T>());
+}
+
+template <typename T>
+T *as_raw_ptr_release_ownership(smart_holder &hld,
+                                const char *context = "as_raw_ptr_release_ownership") {
+    hld.ensure_can_release_ownership(context);
+    T *raw_ptr = hld.as_raw_ptr_unowned<T>();
+    hld.release_ownership();
+    return raw_ptr;
+}
+
+template <typename T, typename D = std::default_delete<T>>
+std::unique_ptr<T, D> as_unique_ptr(smart_holder &hld) {
+    static const char *context = "as_unique_ptr";
+    hld.ensure_compatible_rtti_uqp_del<T, D>(context);
+    hld.ensure_use_count_1(context);
+    T *raw_ptr = hld.as_raw_ptr_unowned<T>();
+    hld.release_ownership();
+    // KNOWN DEFECT (see PR #4850): Does not copy the deleter.
+    return std::unique_ptr<T, D>(raw_ptr);
+}
+
+} // namespace smart_holder_poc
+} // namespace memory
+} // namespace pybindit
diff --git a/tests/pure_cpp/smart_holder_poc_test.cpp b/tests/pure_cpp/smart_holder_poc_test.cpp
index a9ad0364e..24ab643ee 100644
--- a/tests/pure_cpp/smart_holder_poc_test.cpp
+++ b/tests/pure_cpp/smart_holder_poc_test.cpp
@@ -1,6 +1,4 @@
-#define PYBIND11_TESTS_PURE_CPP_SMART_HOLDER_POC_TEST_CPP
-
-#include "pybind11/detail/smart_holder_poc.h"
+#include "smart_holder_poc.h"
 
 #include <functional>
 #include <memory>
@@ -16,6 +14,7 @@
 #include "catch.hpp"
 
 using pybindit::memory::smart_holder;
+namespace poc = pybindit::memory::smart_holder_poc;
 
 namespace helpers {
 
@@ -70,14 +69,14 @@ TEST_CASE("from_raw_ptr_unowned+as_raw_ptr_unowned", "[S]") {
 TEST_CASE("from_raw_ptr_unowned+as_lvalue_ref", "[S]") {
     static int value = 19;
     auto hld = smart_holder::from_raw_ptr_unowned(&value);
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
 }
 
 TEST_CASE("from_raw_ptr_unowned+as_rvalue_ref", "[S]") {
     helpers::movable_int orig(19);
     {
         auto hld = smart_holder::from_raw_ptr_unowned(&orig);
-        helpers::movable_int othr(hld.as_rvalue_ref<helpers::movable_int>());
+        helpers::movable_int othr(poc::as_rvalue_ref<helpers::movable_int>(hld));
         REQUIRE(othr.valu == 19);
         REQUIRE(orig.valu == 91);
     }
@@ -86,21 +85,21 @@ TEST_CASE("from_raw_ptr_unowned+as_rvalue_ref", "[S]") {
 TEST_CASE("from_raw_ptr_unowned+as_raw_ptr_release_ownership", "[E]") {
     static int value = 19;
     auto hld = smart_holder::from_raw_ptr_unowned(&value);
-    REQUIRE_THROWS_WITH(hld.as_raw_ptr_release_ownership<int>(),
+    REQUIRE_THROWS_WITH(poc::as_raw_ptr_release_ownership<int>(hld),
                         "Cannot disown non-owning holder (as_raw_ptr_release_ownership).");
 }
 
 TEST_CASE("from_raw_ptr_unowned+as_unique_ptr", "[E]") {
     static int value = 19;
     auto hld = smart_holder::from_raw_ptr_unowned(&value);
-    REQUIRE_THROWS_WITH(hld.as_unique_ptr<int>(),
+    REQUIRE_THROWS_WITH(poc::as_unique_ptr<int>(hld),
                         "Cannot disown non-owning holder (as_unique_ptr).");
 }
 
 TEST_CASE("from_raw_ptr_unowned+as_unique_ptr_with_deleter", "[E]") {
     static int value = 19;
     auto hld = smart_holder::from_raw_ptr_unowned(&value);
-    REQUIRE_THROWS_WITH((hld.as_unique_ptr<int, helpers::functor_builtin_delete<int>>()),
+    REQUIRE_THROWS_WITH((poc::as_unique_ptr<int, helpers::functor_builtin_delete<int>>(hld)),
                         "Missing unique_ptr deleter (as_unique_ptr).");
 }
 
@@ -113,12 +112,12 @@ TEST_CASE("from_raw_ptr_unowned+as_shared_ptr", "[S]") {
 TEST_CASE("from_raw_ptr_take_ownership+as_lvalue_ref", "[S]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
     REQUIRE(hld.has_pointee());
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
 }
 
 TEST_CASE("from_raw_ptr_take_ownership+as_raw_ptr_release_ownership1", "[S]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
-    auto new_owner = std::unique_ptr<int>(hld.as_raw_ptr_release_ownership<int>());
+    auto new_owner = std::unique_ptr<int>(poc::as_raw_ptr_release_ownership<int>(hld));
     REQUIRE(!hld.has_pointee());
     REQUIRE(*new_owner == 19);
 }
@@ -126,13 +125,13 @@ TEST_CASE("from_raw_ptr_take_ownership+as_raw_ptr_release_ownership1", "[S]") {
 TEST_CASE("from_raw_ptr_take_ownership+as_raw_ptr_release_ownership2", "[E]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
     auto shd_ptr = hld.as_shared_ptr<int>();
-    REQUIRE_THROWS_WITH(hld.as_raw_ptr_release_ownership<int>(),
+    REQUIRE_THROWS_WITH(poc::as_raw_ptr_release_ownership<int>(hld),
                         "Cannot disown use_count != 1 (as_raw_ptr_release_ownership).");
 }
 
 TEST_CASE("from_raw_ptr_take_ownership+as_unique_ptr1", "[S]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
-    std::unique_ptr<int> new_owner = hld.as_unique_ptr<int>();
+    std::unique_ptr<int> new_owner = poc::as_unique_ptr<int>(hld);
     REQUIRE(!hld.has_pointee());
     REQUIRE(*new_owner == 19);
 }
@@ -140,12 +139,13 @@ TEST_CASE("from_raw_ptr_take_ownership+as_unique_ptr1", "[S]") {
 TEST_CASE("from_raw_ptr_take_ownership+as_unique_ptr2", "[E]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
     auto shd_ptr = hld.as_shared_ptr<int>();
-    REQUIRE_THROWS_WITH(hld.as_unique_ptr<int>(), "Cannot disown use_count != 1 (as_unique_ptr).");
+    REQUIRE_THROWS_WITH(poc::as_unique_ptr<int>(hld),
+                        "Cannot disown use_count != 1 (as_unique_ptr).");
 }
 
 TEST_CASE("from_raw_ptr_take_ownership+as_unique_ptr_with_deleter", "[E]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
-    REQUIRE_THROWS_WITH((hld.as_unique_ptr<int, helpers::functor_builtin_delete<int>>()),
+    REQUIRE_THROWS_WITH((poc::as_unique_ptr<int, helpers::functor_builtin_delete<int>>(hld)),
                         "Missing unique_ptr deleter (as_unique_ptr).");
 }
 
@@ -160,14 +160,14 @@ TEST_CASE("from_raw_ptr_take_ownership+disown+reclaim_disowned", "[S]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
     std::unique_ptr<int> new_owner(hld.as_raw_ptr_unowned<int>());
     hld.disown();
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
     REQUIRE(*new_owner == 19);
     hld.reclaim_disowned(); // Manually veriified: without this, clang++ -fsanitize=address reports
                             // "detected memory leaks".
     // NOLINTNEXTLINE(bugprone-unused-return-value)
     (void) new_owner.release(); // Manually verified: without this, clang++ -fsanitize=address
                                 // reports "attempting double-free".
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
     REQUIRE(new_owner.get() == nullptr);
 }
 
@@ -175,7 +175,7 @@ TEST_CASE("from_raw_ptr_take_ownership+disown+release_disowned", "[S]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
     std::unique_ptr<int> new_owner(hld.as_raw_ptr_unowned<int>());
     hld.disown();
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
     REQUIRE(*new_owner == 19);
     hld.release_disowned();
     REQUIRE(!hld.has_pointee());
@@ -195,14 +195,14 @@ TEST_CASE("from_unique_ptr+as_lvalue_ref", "[S]") {
     std::unique_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
 }
 
 TEST_CASE("from_unique_ptr+as_raw_ptr_release_ownership1", "[S]") {
     std::unique_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    auto new_owner = std::unique_ptr<int>(hld.as_raw_ptr_release_ownership<int>());
+    auto new_owner = std::unique_ptr<int>(poc::as_raw_ptr_release_ownership<int>(hld));
     REQUIRE(!hld.has_pointee());
     REQUIRE(*new_owner == 19);
 }
@@ -212,7 +212,7 @@ TEST_CASE("from_unique_ptr+as_raw_ptr_release_ownership2", "[E]") {
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
     auto shd_ptr = hld.as_shared_ptr<int>();
-    REQUIRE_THROWS_WITH(hld.as_raw_ptr_release_ownership<int>(),
+    REQUIRE_THROWS_WITH(poc::as_raw_ptr_release_ownership<int>(hld),
                         "Cannot disown use_count != 1 (as_raw_ptr_release_ownership).");
 }
 
@@ -220,7 +220,7 @@ TEST_CASE("from_unique_ptr+as_unique_ptr1", "[S]") {
     std::unique_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    std::unique_ptr<int> new_owner = hld.as_unique_ptr<int>();
+    std::unique_ptr<int> new_owner = poc::as_unique_ptr<int>(hld);
     REQUIRE(!hld.has_pointee());
     REQUIRE(*new_owner == 19);
 }
@@ -230,14 +230,15 @@ TEST_CASE("from_unique_ptr+as_unique_ptr2", "[E]") {
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
     auto shd_ptr = hld.as_shared_ptr<int>();
-    REQUIRE_THROWS_WITH(hld.as_unique_ptr<int>(), "Cannot disown use_count != 1 (as_unique_ptr).");
+    REQUIRE_THROWS_WITH(poc::as_unique_ptr<int>(hld),
+                        "Cannot disown use_count != 1 (as_unique_ptr).");
 }
 
 TEST_CASE("from_unique_ptr+as_unique_ptr_with_deleter", "[E]") {
     std::unique_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    REQUIRE_THROWS_WITH((hld.as_unique_ptr<int, helpers::functor_builtin_delete<int>>()),
+    REQUIRE_THROWS_WITH((poc::as_unique_ptr<int, helpers::functor_builtin_delete<int>>(hld)),
                         "Incompatible unique_ptr deleter (as_unique_ptr).");
 }
 
@@ -254,7 +255,7 @@ TEST_CASE("from_unique_ptr_derived+as_unique_ptr_base", "[S]") {
     std::unique_ptr<helpers::derived> orig_owner(new helpers::derived());
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    std::unique_ptr<helpers::base> new_owner = hld.as_unique_ptr<helpers::base>();
+    std::unique_ptr<helpers::base> new_owner = poc::as_unique_ptr<helpers::base>(hld);
     REQUIRE(!hld.has_pointee());
     REQUIRE(new_owner->get() == 100);
 }
@@ -265,7 +266,7 @@ TEST_CASE("from_unique_ptr_derived+as_unique_ptr_base2", "[E]") {
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
     REQUIRE_THROWS_WITH(
-        (hld.as_unique_ptr<helpers::base, helpers::functor_builtin_delete<helpers::base>>()),
+        (poc::as_unique_ptr<helpers::base, helpers::functor_builtin_delete<helpers::base>>(hld)),
         "Incompatible unique_ptr deleter (as_unique_ptr).");
 }
 
@@ -273,7 +274,7 @@ TEST_CASE("from_unique_ptr_with_deleter+as_lvalue_ref", "[S]") {
     std::unique_ptr<int, helpers::functor_builtin_delete<int>> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
 }
 
 TEST_CASE("from_unique_ptr_with_std_function_deleter+as_lvalue_ref", "[S]") {
@@ -281,14 +282,14 @@ TEST_CASE("from_unique_ptr_with_std_function_deleter+as_lvalue_ref", "[S]") {
         new int(19), [](const int *raw_ptr) { delete raw_ptr; });
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
 }
 
 TEST_CASE("from_unique_ptr_with_deleter+as_raw_ptr_release_ownership", "[E]") {
     std::unique_ptr<int, helpers::functor_builtin_delete<int>> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    REQUIRE_THROWS_WITH(hld.as_raw_ptr_release_ownership<int>(),
+    REQUIRE_THROWS_WITH(poc::as_raw_ptr_release_ownership<int>(hld),
                         "Cannot disown custom deleter (as_raw_ptr_release_ownership).");
 }
 
@@ -296,7 +297,7 @@ TEST_CASE("from_unique_ptr_with_deleter+as_unique_ptr", "[E]") {
     std::unique_ptr<int, helpers::functor_builtin_delete<int>> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    REQUIRE_THROWS_WITH(hld.as_unique_ptr<int>(),
+    REQUIRE_THROWS_WITH(poc::as_unique_ptr<int>(hld),
                         "Incompatible unique_ptr deleter (as_unique_ptr).");
 }
 
@@ -305,7 +306,7 @@ TEST_CASE("from_unique_ptr_with_deleter+as_unique_ptr_with_deleter1", "[S]") {
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
     std::unique_ptr<int, helpers::functor_builtin_delete<int>> new_owner
-        = hld.as_unique_ptr<int, helpers::functor_builtin_delete<int>>();
+        = poc::as_unique_ptr<int, helpers::functor_builtin_delete<int>>(hld);
     REQUIRE(!hld.has_pointee());
     REQUIRE(*new_owner == 19);
 }
@@ -314,7 +315,7 @@ TEST_CASE("from_unique_ptr_with_deleter+as_unique_ptr_with_deleter2", "[E]") {
     std::unique_ptr<int, helpers::functor_builtin_delete<int>> orig_owner(new int(19));
     auto hld = smart_holder::from_unique_ptr(std::move(orig_owner));
     REQUIRE(orig_owner.get() == nullptr);
-    REQUIRE_THROWS_WITH((hld.as_unique_ptr<int, helpers::functor_other_delete<int>>()),
+    REQUIRE_THROWS_WITH((poc::as_unique_ptr<int, helpers::functor_other_delete<int>>(hld)),
                         "Incompatible unique_ptr deleter (as_unique_ptr).");
 }
 
@@ -330,27 +331,27 @@ TEST_CASE("from_unique_ptr_with_deleter+as_shared_ptr", "[S]") {
 TEST_CASE("from_shared_ptr+as_lvalue_ref", "[S]") {
     std::shared_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_shared_ptr(orig_owner);
-    REQUIRE(hld.as_lvalue_ref<int>() == 19);
+    REQUIRE(poc::as_lvalue_ref<int>(hld) == 19);
 }
 
 TEST_CASE("from_shared_ptr+as_raw_ptr_release_ownership", "[E]") {
     std::shared_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_shared_ptr(orig_owner);
-    REQUIRE_THROWS_WITH(hld.as_raw_ptr_release_ownership<int>(),
+    REQUIRE_THROWS_WITH(poc::as_raw_ptr_release_ownership<int>(hld),
                         "Cannot disown external shared_ptr (as_raw_ptr_release_ownership).");
 }
 
 TEST_CASE("from_shared_ptr+as_unique_ptr", "[E]") {
     std::shared_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_shared_ptr(orig_owner);
-    REQUIRE_THROWS_WITH(hld.as_unique_ptr<int>(),
+    REQUIRE_THROWS_WITH(poc::as_unique_ptr<int>(hld),
                         "Cannot disown external shared_ptr (as_unique_ptr).");
 }
 
 TEST_CASE("from_shared_ptr+as_unique_ptr_with_deleter", "[E]") {
     std::shared_ptr<int> orig_owner(new int(19));
     auto hld = smart_holder::from_shared_ptr(orig_owner);
-    REQUIRE_THROWS_WITH((hld.as_unique_ptr<int, helpers::functor_builtin_delete<int>>()),
+    REQUIRE_THROWS_WITH((poc::as_unique_ptr<int, helpers::functor_builtin_delete<int>>(hld)),
                         "Missing unique_ptr deleter (as_unique_ptr).");
 }
 
@@ -362,19 +363,19 @@ TEST_CASE("from_shared_ptr+as_shared_ptr", "[S]") {
 
 TEST_CASE("error_unpopulated_holder", "[E]") {
     smart_holder hld;
-    REQUIRE_THROWS_WITH(hld.as_lvalue_ref<int>(), "Unpopulated holder (as_lvalue_ref).");
+    REQUIRE_THROWS_WITH(poc::as_lvalue_ref<int>(hld), "Unpopulated holder (as_lvalue_ref).");
 }
 
 TEST_CASE("error_disowned_holder", "[E]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
-    hld.as_unique_ptr<int>();
-    REQUIRE_THROWS_WITH(hld.as_lvalue_ref<int>(), "Disowned holder (as_lvalue_ref).");
+    poc::as_unique_ptr<int>(hld);
+    REQUIRE_THROWS_WITH(poc::as_lvalue_ref<int>(hld), "Disowned holder (as_lvalue_ref).");
 }
 
 TEST_CASE("error_cannot_disown_nullptr", "[E]") {
     auto hld = smart_holder::from_raw_ptr_take_ownership(new int(19));
-    hld.as_unique_ptr<int>();
-    REQUIRE_THROWS_WITH(hld.as_unique_ptr<int>(), "Cannot disown nullptr (as_unique_ptr).");
+    poc::as_unique_ptr<int>(hld);
+    REQUIRE_THROWS_WITH(poc::as_unique_ptr<int>(hld), "Cannot disown nullptr (as_unique_ptr).");
 }
 
 TEST_CASE("indestructible_int-from_raw_ptr_unowned+as_raw_ptr_unowned", "[S]") {