tagged rework (#110)

* Implement ericniebler/stl2#299
* Implement ericniebler/stl2#363
* Implement ericniebler/stl2#364
* Implement ericniebler/stl2#418
* Remove tuple_find that was dropped from variant ages ago
* Implement extension 'structible object concepts
* tighten up constrains in the tagged impl

include/stl2/detail/concepts/object.hpp

@@ -54,6 +54,24 @@ STL2_OPEN_NAMESPACE {
 
 
 	namespace ext {
+		///////////////////////////////////////////////////////////////////////////
+		// 'structible object concepts
+		//
+		template <class T>
+		concept bool DestructibleObject = Object<T> && Destructible<T>;
+
+		template <class T, class... Args>
+		concept bool ConstructibleObject = Object<T> && Constructible<T, Args...>;
+
+		template <class T>
+		concept bool DefaultConstructibleObject = Object<T> && DefaultConstructible<T>;
+
+		template <class T>
+		concept bool MoveConstructibleObject = Object<T> && MoveConstructible<T>;
+
+		template <class T>
+		concept bool CopyConstructibleObject = Object<T> && CopyConstructible<T>;
+
 		///////////////////////////////////////////////////////////////////////////
 		// TriviallyFoo concepts
 		//

include/stl2/detail/concepts/object/movable.hpp

@@ -26,7 +26,7 @@ STL2_OPEN_NAMESPACE {
 	// https://github.com/ericniebler/stl2/issues/310
 	template <class T>
 	concept bool Movable =
-		_Is<T, is_object> &&
+		ext::Object<T> &&
 		MoveConstructible<T> &&
 		Assignable<T&, T&&> &&
 		Swappable<T>;
@@ -36,7 +36,7 @@ STL2_OPEN_NAMESPACE {
 		constexpr bool Movable = false;
 		__stl2::Movable{T}
 		constexpr bool Movable<T> = true;
-	}
+	} // namespace models
 } STL2_CLOSE_NAMESPACE
 
 #endif

include/stl2/detail/concepts/object/move_constructible.hpp

@@ -19,6 +19,21 @@
 #include <stl2/detail/concepts/core.hpp>
 
 STL2_OPEN_NAMESPACE {
+	///////////////////////////////////////////////////////////////////////////
+	// Object [Extension]
+	//
+	namespace ext {
+		template <class T>
+		concept bool Object = _Is<T, std::is_object>;
+	} // namespace ext
+
+	namespace models {
+		template <class>
+		constexpr bool Object = false;
+		__stl2::ext::Object{T}
+		constexpr bool Object<T> = true;
+	} // namespace models
+
 	///////////////////////////////////////////////////////////////////////////
 	// Addressable [Extension]
 	//
@@ -34,7 +49,7 @@ STL2_OPEN_NAMESPACE {
 	namespace ext {
 		template <class T>
 		concept bool Addressable =
-			_Is<T, is_object> && __addressable<T>;
+			Object<T> && __addressable<T>;
 	}
 
 	namespace models {

include/stl2/detail/ebo_box.hpp

@@ -19,8 +19,7 @@
 
 STL2_OPEN_NAMESPACE {
 	namespace detail {
-		template <Destructible T, class Tag = void>
-		requires std::is_object<T>::value
+		template <ext::DestructibleObject T, class Tag = void>
 		struct ebo_box {
 			ebo_box() = default;
 			constexpr ebo_box(const T& t)
@@ -58,9 +57,8 @@ STL2_OPEN_NAMESPACE {
 			T item_;
 		};
 
-		template <Destructible T, class Tag>
-		requires std::is_object<T>::value &&
-			std::is_empty<T>::value && !std::is_final<T>::value
+		template <ext::DestructibleObject T, class Tag>
+		requires std::is_empty<T>::value && !std::is_final<T>::value
 		struct ebo_box<T, Tag> : private T {
 			ebo_box() = default;
 			constexpr ebo_box(const T& t)

include/stl2/detail/functional/invoke.hpp

@@ -15,6 +15,7 @@
 #include <stl2/detail/fwd.hpp>
 #include <stl2/detail/meta.hpp>
 #include <stl2/detail/concepts/core.hpp>
+#include <stl2/detail/concepts/object.hpp>
 
 STL2_OPEN_NAMESPACE {
 	///////////////////////////////////////////////////////////////////////////
@@ -61,10 +62,10 @@ STL2_OPEN_NAMESPACE {
 			(coerce<T>(std::forward<T1>(t1)).*f)(std::forward<Args>(args)...)
 		)
 
-		template <_Is<is_object> D, class T, class T1>
+		template <ext::Object D, class T, class T1>
 		constexpr decltype(auto) impl(D (T::*f), T1&& t1) = delete;
 
-		template <_Is<is_object> D, class T, class T1>
+		template <ext::Object D, class T, class T1>
 		requires
 			requires(D (T::*f), T1&& t1) {
 				coerce<T>(std::forward<T1>(t1)).*f;

include/stl2/detail/iterator/concepts.hpp

@@ -124,9 +124,10 @@ STL2_OPEN_NAMESPACE {
 	template <class>
 	struct value_type {};
 
-	template <class T>
-	struct value_type<T*> :
-		meta::lazy::if_<is_object<T>, remove_cv_t<T>> {};
+	template <ext::Object T>
+	struct value_type<T*> {
+		using type = std::remove_cv_t<T>;
+	};
 
 	template <_Is<is_array> T>
 	struct value_type<T> : value_type<decay_t<T>> {};
@@ -135,13 +136,21 @@ STL2_OPEN_NAMESPACE {
 	struct value_type<I const> : value_type<decay_t<I>> {};
 
 	template <detail::MemberValueType T>
+	struct value_type<T> {};
+
+	template <detail::MemberValueType T>
+	requires ext::Object<typename T::value_type>
 	struct value_type<T> {
 		using type = typename T::value_type;
 	};
 
 	template <detail::MemberElementType T>
+	struct value_type<T> {};
+
+	template <detail::MemberElementType T>
+	requires ext::Object<std::remove_cv_t<typename T::element_type>>
 	struct value_type<T> {
-		using type = typename T::element_type;
+		using type = std::remove_cv_t<typename T::element_type>;
 	};
 
 	///////////////////////////////////////////////////////////////////////////

include/stl2/detail/iterator/increment.hpp

@@ -38,9 +38,10 @@ STL2_OPEN_NAMESPACE {
 
 	template <class> struct difference_type {};
 
-	template <class T>
-	struct difference_type<T*>
-	: meta::lazy::if_<std::is_object<T>, std::ptrdiff_t> {};
+	template <ext::Object T>
+	struct difference_type<T*> {
+		using type = std::ptrdiff_t;
+	};
 
 	template <class T>
 	struct difference_type<const T>

include/stl2/detail/semiregular_box.hpp

@@ -20,8 +20,7 @@
 
 STL2_OPEN_NAMESPACE {
 	namespace detail {
-		template <Destructible T>
-		requires _Is<T, is_object>
+		template <ext::DestructibleObject T>
 		class semiregular_box {
 		public:
 			semiregular_box() = default;