Synopsis with full class definitions

Author: polytypic

provides/include/dumpster_v1/finally.hpp

@@ -4,19 +4,21 @@
 
 #include <utility>
 
-template <class Action> struct dumpster_v1::finally_t {
-  ~finally_t() { m_action(); }
+template <class Action> dumpster_v1::Private::finally_t<Action>::~finally_t() {
+  m_action();
+}
 
-  template <class ForwardableAction>
-  finally_t(ForwardableAction &&action)
-      : m_action(std::forward<ForwardableAction>(action)) {}
+template <class Action>
+template <class ForwardableAction>
+dumpster_v1::Private::finally_t<Action>::finally_t(ForwardableAction &&action)
+    : m_action(std::forward<ForwardableAction>(action)) {}
 
-  finally_t(const finally_t &) = delete;
-  finally_t operator=(const finally_t &) = delete;
+template <class Action> dumpster_v1::finally_t<Action>::~finally_t() {}
 
-private:
-  std::conditional_t<std::is_function_v<Action>, Action *, Action> m_action;
-};
+template <class Action>
+template <class ForwardableAction>
+dumpster_v1::finally_t<Action>::finally_t(ForwardableAction &&action)
+    : Private::finally_t<Action>(std::forward<ForwardableAction>(action)) {}
 
 template <class Action>
 dumpster_v1::finally_t<std::remove_cvref_t<Action>>

provides/include/dumpster_v1/private.hpp

@@ -0,0 +1,25 @@
+#pragma once
+
+#include "polyfill_v1/type_traits.hpp"
+
+namespace dumpster_v1 {
+
+template <class Value> struct finally_t;
+
+class Private {
+  template <class> friend struct finally_t;
+
+  template <class Value> class finally_t;
+};
+
+} // namespace dumpster_v1
+
+template <class Action> class dumpster_v1::Private::finally_t {
+  template <class> friend struct dumpster_v1::finally_t;
+
+  ~finally_t();
+
+  template <class ForwardableAction> finally_t(ForwardableAction &&action);
+
+  std::conditional_t<std::is_function_v<Action>, Action *, Action> m_action;
+};

provides/include/dumpster_v1/synopsis.hpp

@@ -1,13 +1,25 @@
 #pragma once
 
-#include "polyfill_v1/type_traits.hpp"
+#include "dumpster_v1/private.hpp"
 
 namespace dumpster_v1 {
 
 // finally.hpp =================================================================
 
 /// Finalizer that invokes stored action when destroyed.
-template <class Action> struct finally_t;
+template <class Action> struct finally_t : Private::finally_t<Action> {
+  /// Calls the finalizing action given to the constructor.
+  ~finally_t();
+
+  /// Constructs a finalizer from the given finalizing action.
+  template <class ForwardableAction> finally_t(ForwardableAction &&action);
+
+  /// Finalizers are not CopyConstructible.
+  finally_t(const finally_t &) = delete;
+
+  /// Finalizers are not CopyAssignable.
+  finally_t &operator=(const finally_t &) = delete;
+};
 
 /// Creates a finalizer that invokes the action when destroyed.
 template <class Action>