refactor: clean up factory & compressed pair

6 files changed, 297 insertions, 223 deletions

diff --git a/include/yacppdic/detail/factory-impl.hpp b/include/yacppdic/detail/factory-impl.hpp
index 3deede2..c6da207 100644
--- a/include/yacppdic/detail/factory-impl.hpp
+++ b/include/yacppdic/detail/factory-impl.hpp
@@ -5,18 +5,19 @@
 namespace yacppdic
 {
 
-template <class Return, class... Args>
-Factory<Return(Args...)>::Factory(const Factory &factory) : _functor(factory._functor)
+template <typename Return, typename... Args>
+Factory<Return(Args...)>::Factory(const Factory &factory) noexcept
+	: _functor(factory._functor)
 {
 }
 
-template <class Return, class... Args>
+template <typename Return, typename... Args>
 Factory<Return(Args...)>::Factory(Factory &&factory) noexcept
 	: _functor(std::move(factory._functor))
 {
 }
 
-template <class Return, class... Args>
+template <typename Return, typename... Args>
 auto Factory<Return(Args...)>::operator=(Factory &&factory) noexcept
 	-> Factory<Return(Args...)> &
 {
@@ -24,7 +25,7 @@ auto Factory<Return(Args...)>::operator=(Factory &&factory) noexcept
 	return *this;
 }
 
-template <class Return, class... Args>
+template <typename Return, typename... Args>
 auto Factory<Return(Args...)>::operator=(std::nullptr_t) noexcept
 	-> Factory<Return(Args...)> &
 {
@@ -32,39 +33,88 @@ auto Factory<Return(Args...)>::operator=(std::nullptr_t) noexcept
 	return *this;
 }
 
-template <class Return, class... Args>
-Factory<Return(Args...)>::~Factory() = default;
-
-template <class Return, class... Args>
+template <typename Return, typename... Args>
 Factory<Return(Args...)>::operator bool() const noexcept
 {
 	return static_cast<bool>(_functor);
 }
 
-template <class Return, class... Args>
-auto Factory<Return(Args...)>::operator()(Args... args) const -> Return
+template <typename Return, typename... Args>
+auto Factory<Return(Args...)>::operator()(Args... args) const noexcept -> Return
 {
 	return _functor(std::forward<Args>(args)...);
 }
 
-template <class Return, class... Args>
+template <typename Return, typename... Args>
 auto Factory<Return(Args...)>::target_type() const noexcept -> const std::type_info &
 {
 	return _functor.target_type();
 }
 
-template <class Return, class... Args>
+template <typename Return, typename... Args>
 template <typename Tp>
 auto Factory<Return(Args...)>::target() noexcept -> Tp *
 {
 	return static_cast<Tp *>(_functor.template target<Tp>());
 }
 
-template <class Return, class... Args>
+template <typename Return, typename... Args>
 template <typename Tp>
 auto Factory<Return(Args...)>::target() const noexcept -> const Tp *
 {
 	return _functor.template target<Tp>();
 }
 
+template <typename Return, typename... Args>
+inline auto operator==(const Factory<Return(Args...)> &factory, std::nullptr_t) noexcept
+	-> bool
+{
+	return !factory;
+}
+
+template <typename Return, typename... Args>
+inline auto operator==(std::nullptr_t, const Factory<Return(Args...)> &factory) noexcept
+	-> bool
+{
+	return !factory;
+}
+
+template <typename Return, typename... Args>
+inline auto operator!=(const Factory<Return(Args...)> &factory, std::nullptr_t) noexcept
+	-> bool
+{
+	return static_cast<bool>(factory);
+}
+
+template <typename Return, typename... Args>
+inline auto operator!=(std::nullptr_t, const Factory<Return(Args...)> &factory) noexcept
+	-> bool
+{
+	return static_cast<bool>(factory);
+}
+
+} // namespace yacppdic
+
+template <typename Function>
+constexpr auto not_null(Function const & /*unused*/) -> bool
+{
+	return true;
+}
+
+template <typename Function>
+constexpr auto not_null(Function *function_ptr) -> bool
+{
+	return function_ptr;
+}
+
+template <typename Return, typename Class>
+constexpr auto not_null(Return Class::*method_ptr) -> bool
+{
+	return method_ptr;
+}
+
+template <typename Function>
+constexpr auto not_null(yacppdic::Factory<Function> const &factory) -> bool
+{
+	return !!factory;
 }
diff --git a/include/yacppdic/detail/internal/compressed_pair-impl.hpp b/include/yacppdic/detail/internal/compressed_pair-impl.hpp
index 0e2a322..9a458e4 100644
--- a/include/yacppdic/detail/internal/compressed_pair-impl.hpp
+++ b/include/yacppdic/detail/internal/compressed_pair-impl.hpp
@@ -5,42 +5,94 @@
 namespace yacppdic::internal
 {
 
-template <class Value, int Idx>
-constexpr CompressedPairElement<Value, Idx>::CompressedPairElement(
-	DefaultInitTag /*default_init_tag*/
-)
+template <typename ValueOne, typename ValueTwo>
+requires NotSameAs<ValueOne, ValueTwo>
+template <typename>
+requires std::default_initializable<ValueOne> && std::default_initializable<ValueTwo>
+constexpr CompressedPair<ValueOne, ValueTwo>::CompressedPair() noexcept
+	: BaseOne(ValueInitTag()), BaseTwo(ValueInitTag())
 {
 }
 
-template <class Value, int Idx>
-constexpr CompressedPairElement<Value, Idx>::CompressedPairElement(
-	ValueInitTag /*value_init_tag*/
-)
-	: _value()
+template <typename ValueOne, typename ValueTwo>
+requires NotSameAs<ValueOne, ValueTwo>
+template <typename FirstValue, typename SecondValue>
+constexpr CompressedPair<ValueOne, ValueTwo>::CompressedPair(
+	FirstValue &&first_value,
+	SecondValue &&second_value
+) noexcept
+	: BaseOne(std::forward<FirstValue>(first_value)),
+	  BaseTwo(std::forward<SecondValue>(second_value))
 {
 }
 
-template <class Value, int Idx>
-template <class... Args, size_t... Indices>
-constexpr CompressedPairElement<Value, Idx>::CompressedPairElement(
-	std::piecewise_construct_t /*tag_types*/,
-	std::tuple<Args...> args,
-	TupleIndices<Indices...> /*indices*/
-)
-	: _value(std::forward<Args>(std::get<Indices>(args))...)
+template <typename ValueOne, typename ValueTwo>
+requires NotSameAs<ValueOne, ValueTwo>
+template <typename... ArgsOne, typename... ArgsTwo>
+constexpr CompressedPair<ValueOne, ValueTwo>::CompressedPair(
+	std::piecewise_construct_t piecewise_construct,
+	std::tuple<ArgsOne...> first_args,
+	std::tuple<ArgsTwo...> second_args
+) noexcept
+	: BaseOne(
+		  piecewise_construct,
+		  std::move(first_args),
+		  typename MakeTupleIndices<sizeof...(ArgsOne)>::type()
+	  ),
+	  BaseTwo(
+		  piecewise_construct,
+		  std::move(second_args),
+		  typename MakeTupleIndices<sizeof...(ArgsTwo)>::type()
+	  )
 {
 }
 
-template <class Value, int Idx>
-auto CompressedPairElement<Value, Idx>::get() noexcept -> ValueReference
+template <typename ValueOne, typename ValueTwo>
+requires NotSameAs<ValueOne, ValueTwo>
+auto CompressedPair<ValueOne, ValueTwo>::first() noexcept ->
+	typename BaseOne::ValueReference
 {
-	return _value;
+	return static_cast<BaseOne &>(*this).get();
 }
 
-template <class Value, int Idx>
-auto CompressedPairElement<Value, Idx>::get() const noexcept -> ConstValueReference
+template <typename ValueOne, typename ValueTwo>
+requires NotSameAs<ValueOne, ValueTwo>
+auto CompressedPair<ValueOne, ValueTwo>::first() const noexcept ->
+	typename BaseOne::ConstValueReference
 {
-	return _value;
+	return static_cast<BaseOne const &>(*this).get();
+}
+
+template <typename ValueOne, typename ValueTwo>
+requires NotSameAs<ValueOne, ValueTwo>
+auto CompressedPair<ValueOne, ValueTwo>::second() noexcept ->
+	typename BaseTwo::ValueReference
+{
+	return static_cast<BaseTwo &>(*this).get();
+}
+
+template <typename ValueOne, typename ValueTwo>
+requires NotSameAs<ValueOne, ValueTwo>
+auto CompressedPair<ValueOne, ValueTwo>::second() const noexcept ->
+	typename BaseTwo::ConstValueReference
+{
+	return static_cast<BaseTwo const &>(*this).get();
+}
+
+template <typename ValueOne, typename ValueTwo>
+requires NotSameAs<ValueOne, ValueTwo>
+constexpr auto CompressedPair<ValueOne, ValueTwo>::get_first_base(CompressedPair *pair
+) noexcept -> BaseOne *
+{
+	return static_cast<BaseOne *>(pair);
+}
+
+template <typename ValueOne, typename ValueTwo>
+requires NotSameAs<ValueOne, ValueTwo>
+constexpr auto CompressedPair<ValueOne, ValueTwo>::get_second_base(CompressedPair *pair
+) noexcept -> BaseTwo *
+{
+	return static_cast<BaseTwo *>(pair);
 }
 
 } // namespace yacppdic::internal
diff --git a/include/yacppdic/detail/internal/compressed_pair.hpp b/include/yacppdic/detail/internal/compressed_pair.hpp
index 3c832c5..7d98bbd 100644
--- a/include/yacppdic/detail/internal/compressed_pair.hpp
+++ b/include/yacppdic/detail/internal/compressed_pair.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include "yacppdic/detail/internal/misc_concepts.hpp"
+#include "yacppdic/detail/internal/tuple_indices.hpp"
 
 #include <concepts>
 #include <tuple>
@@ -11,104 +12,94 @@ namespace yacppdic::internal
 {
 
 // Tag used to default initialize one or both of the pair's elements.
-struct DefaultInitTag
+class DefaultInitTag
 {
 };
 
-struct ValueInitTag
+class ValueInitTag
 {
 };
 
-template <size_t...>
-struct TupleIndices
-{
-};
-
-template <class IdxType, IdxType... Values>
-struct IntegerSequence
-{
-	template <template <class OIdxType, OIdxType...> class ToIndexSeq, class ToIndexType>
-	using Convert = ToIndexSeq<ToIndexType, Values...>;
-
-	template <size_t Sp>
-	using ToTupleIndices = TupleIndices<(Values + Sp)...>;
-};
-
-template <size_t SizeOne, size_t SizeTwo>
-using MakeIndices =
-	typename __make_integer_seq<IntegerSequence, size_t, SizeOne - SizeTwo>::
-		template ToTupleIndices<SizeTwo>;
-
-template <size_t SizeOne, size_t SizeTwo = 0>
-requires(SizeTwo <= SizeOne) struct MakeTupleIndices
-{
-	using type = MakeIndices<SizeOne, SizeTwo>;
-};
-
 template <typename Value>
 concept ValueCanBeEmptyBase = std::is_empty_v<Value> && !std::is_final_v<Value>;
 
-template <class Value, int Idx>
+template <typename Value, int Idx>
 class CompressedPairElement
 {
 public:
 	using ValueReference = Value &;
 	using ConstValueReference = const Value &;
 
-	constexpr explicit CompressedPairElement(DefaultInitTag default_init_tag);
+	constexpr explicit CompressedPairElement(DefaultInitTag /*default_init_tag*/
+	) noexcept {};
 
-	constexpr explicit CompressedPairElement(ValueInitTag value_init_tag);
+	constexpr explicit CompressedPairElement(ValueInitTag /*value_init_tag*/) noexcept
+		: _value()
+	{
+	}
 
-	template <class ElementValue>
+	template <typename ElementValue>
 	requires std::same_as<CompressedPairElement, std::decay_t<ElementValue>>
 	// NOLINTNEXTLINE(bugprone-forwarding-reference-overload)
-	constexpr explicit CompressedPairElement(ElementValue &&value)
+	constexpr explicit CompressedPairElement(ElementValue &&value) noexcept
 		: _value(std::forward<ElementValue>(value))
 	{
 	}
 
-	template <class... Args, size_t... Indices>
+	template <typename... Args, std::size_t... Indices>
 	constexpr CompressedPairElement(
-		std::piecewise_construct_t tag_type,
+		std::piecewise_construct_t /*tag_type*/,
 		std::tuple<Args...> args,
-		TupleIndices<Indices...> tuple_indices
-	);
+		TupleIndices<Indices...> /*tuple_indices*/
+	) noexcept
+		: _value(std::forward<Args>(std::get<Indices>(args))...)
+	{
+	}
 
-	auto get() noexcept -> ValueReference;
+	auto get() noexcept -> ValueReference
+	{
+		return _value;
+	}
 
-	[[nodiscard]] auto get() const noexcept -> ConstValueReference;
+	[[nodiscard]] auto get() const noexcept -> ConstValueReference
+	{
+		return _value;
+	}
 
 private:
 	Value _value;
 };
 
-template <class Value, int Idx>
+template <typename Value, int Idx>
 requires ValueCanBeEmptyBase<Value>
-struct CompressedPairElement<Value, Idx> : private Value
+class CompressedPairElement<Value, Idx> : private Value
 {
+public:
 	using ValueReference = Value &;
 	using ConstValueReference = const Value &;
 
-	constexpr CompressedPairElement() = default;
+	constexpr CompressedPairElement() noexcept = default;
 
-	constexpr explicit CompressedPairElement(DefaultInitTag /*unused*/) {}
+	constexpr explicit CompressedPairElement(DefaultInitTag /*unused*/) noexcept {}
 
-	constexpr explicit CompressedPairElement(ValueInitTag /*unused*/) : Value() {}
+	constexpr explicit CompressedPairElement(ValueInitTag /*unused*/) noexcept : Value()
+	{
+	}
 
-	template <class ElementValue>
+	template <typename ElementValue>
 	requires std::same_as<CompressedPairElement, typename std::decay<ElementValue>::type>
 	// NOLINTNEXTLINE(bugprone-forwarding-reference-overload)
-	constexpr explicit CompressedPairElement(ElementValue &&value)
+	constexpr explicit CompressedPairElement(ElementValue &&value) noexcept
 		: Value(std::forward<ElementValue>(value))
 	{
 	}
 
-	template <class... Args, size_t... Indices>
+	template <typename... Args, std::size_t... Indices>
 	constexpr CompressedPairElement(
 		std::piecewise_construct_t /*unused*/,
 		std::tuple<Args...> args,
 		TupleIndices<Indices...> /*unused*/
-	)
+	) noexcept
 		: Value(std::forward<Args>(std::get<Indices>(args))...)
 	{
 	}
@@ -124,7 +115,7 @@ struct CompressedPairElement<Value, Idx> : private Value
 	}
 };
 
-template <class ValueOne, class ValueTwo>
+template <typename ValueOne, typename ValueTwo>
 requires NotSameAs<ValueOne, ValueTwo>
 class CompressedPair : private CompressedPairElement<ValueOne, 0>,
 					   private CompressedPairElement<ValueTwo, 1>
@@ -135,63 +126,32 @@ public:
 
 	template <typename>
 	requires std::default_initializable<ValueOne> && std::default_initializable<ValueTwo>
-	constexpr CompressedPair() : BaseOne(ValueInitTag()), BaseTwo(ValueInitTag()) {}
+	constexpr CompressedPair() noexcept;
 
-	template <class FirstValue, class SecondValue>
-	constexpr CompressedPair(FirstValue &&first_value, SecondValue &&second_value)
-		: BaseOne(std::forward<FirstValue>(first_value)),
-		  BaseTwo(std::forward<SecondValue>(second_value))
-	{
-	}
+	template <typename FirstValue, typename SecondValue>
+	constexpr CompressedPair(
+		FirstValue &&first_value,
+		SecondValue &&second_value
+	) noexcept;
 
-	template <class... ArgsOne, class... ArgsTwo>
+	template <typename... ArgsOne, typename... ArgsTwo>
 	constexpr CompressedPair(
 		std::piecewise_construct_t piecewise_construct,
 		std::tuple<ArgsOne...> first_args,
 		std::tuple<ArgsTwo...> second_args
-	)
-		: BaseOne(
-			  piecewise_construct,
-			  std::move(first_args),
-			  typename MakeTupleIndices<sizeof...(ArgsOne)>::type()
-		  ),
-		  BaseTwo(
-			  piecewise_construct,
-			  std::move(second_args),
-			  typename MakeTupleIndices<sizeof...(ArgsTwo)>::type()
-		  )
-	{
-	}
+	) noexcept;
 
-	auto first() noexcept -> typename BaseOne::ValueReference
-	{
-		return static_cast<BaseOne &>(*this).get();
-	}
+	auto first() noexcept -> typename BaseOne::ValueReference;
 
-	[[nodiscard]] auto first() const noexcept -> typename BaseOne::ConstValueReference
-	{
-		return static_cast<BaseOne const &>(*this).get();
-	}
+	[[nodiscard]] auto first() const noexcept -> typename BaseOne::ConstValueReference;
 
-	auto second() noexcept -> typename BaseTwo::ValueReference
-	{
-		return static_cast<BaseTwo &>(*this).get();
-	}
+	auto second() noexcept -> typename BaseTwo::ValueReference;
 
-	[[nodiscard]] auto second() const noexcept -> typename BaseTwo::ConstValueReference
-	{
-		return static_cast<BaseTwo const &>(*this).get();
-	}
+	[[nodiscard]] auto second() const noexcept -> typename BaseTwo::ConstValueReference;
 
-	constexpr static auto get_first_base(CompressedPair *pair) noexcept -> BaseOne *
-	{
-		return static_cast<BaseOne *>(pair);
-	}
+	constexpr static auto get_first_base(CompressedPair *pair) noexcept -> BaseOne *;
 
-	constexpr static auto get_second_base(CompressedPair *pair) noexcept -> BaseTwo *
-	{
-		return static_cast<BaseTwo *>(pair);
-	}
+	constexpr static auto get_second_base(CompressedPair *pair) noexcept -> BaseTwo *;
 };
 
 } // namespace yacppdic::internal
diff --git a/include/yacppdic/detail/internal/factory_base.hpp b/include/yacppdic/detail/internal/factory_base.hpp
new file mode 100644
index 0000000..00c4e4f
--- /dev/null
+++ b/include/yacppdic/detail/internal/factory_base.hpp
@@ -0,0 +1,24 @@
+#pragma once
+
+#include <functional>
+
+template <class Return>
+class MaybeDeriveFromUnaryFunction
+{
+};
+
+template <class Return, class Arg>
+class MaybeDeriveFromUnaryFunction<Return(Arg)> : public std::unary_function<Arg, Return>
+{
+};
+
+template <class Return>
+struct MaybeDeriveFromBinaryFunction
+{
+};
+
+template <class Return, class ArgOne, class ArgTwo>
+struct MaybeDeriveFromBinaryFunction<Return(ArgOne, ArgTwo)>
+	: public std::binary_function<ArgOne, ArgTwo, Return>
+{
+};
diff --git a/include/yacppdic/detail/internal/tuple_indices.hpp b/include/yacppdic/detail/internal/tuple_indices.hpp
new file mode 100644
index 0000000..3a367b6
--- /dev/null
+++ b/include/yacppdic/detail/internal/tuple_indices.hpp
@@ -0,0 +1,39 @@
+#pragma once
+
+#include <cstddef>
+
+namespace yacppdic::internal
+{
+
+template <std::size_t...>
+class TupleIndices
+{
+};
+
+template <typename IdxType, IdxType... Values>
+class IntegerSequence
+{
+public:
+	template <
+		template <typename OIdxType, OIdxType...>
+		typename ToIndexSeq,
+		typename ToIndexType>
+	using Convert = ToIndexSeq<ToIndexType, Values...>;
+
+	template <std::size_t Sp>
+	using ToTupleIndices = TupleIndices<(Values + Sp)...>;
+};
+
+template <std::size_t SizeOne, std::size_t SizeTwo>
+using MakeIndices =
+	typename __make_integer_seq<IntegerSequence, std::size_t, SizeOne - SizeTwo>::
+		template ToTupleIndices<SizeTwo>;
+
+template <std::size_t SizeOne, std::size_t SizeTwo = 0>
+requires(SizeTwo <= SizeOne) class MakeTupleIndices
+{
+public:
+	using type = MakeIndices<SizeOne, SizeTwo>;
+};
+
+} // namespace yacppdic::internal
diff --git a/include/yacppdic/factory.hpp b/include/yacppdic/factory.hpp
index 6de47d8..1eb2dc7 100644
--- a/include/yacppdic/factory.hpp
+++ b/include/yacppdic/factory.hpp
@@ -3,6 +3,7 @@
 #include "yacppdic/detail/internal/interfaces/copyable_functor.hpp"
 
 #include "yacppdic/detail/internal/alloc_destructor.hpp"
+#include "yacppdic/detail/internal/factory_base.hpp"
 #include "yacppdic/detail/internal/functor/alloc_functor.hpp"
 #include "yacppdic/detail/internal/functor/copyable_functor.hpp"
 #include "yacppdic/detail/internal/functor/value_functor.hpp"
@@ -16,62 +17,9 @@
 namespace yacppdic
 {
 
-template <class>
+template <typename>
 class Factory;
 
-}
-
-template <class Function>
-auto not_null(Function const & /*unused*/) -> bool
-{
-	return true;
-}
-
-template <class Function>
-auto not_null(Function *function_ptr) -> bool
-{
-	return function_ptr;
-}
-
-template <class Return, class Class>
-auto not_null(Return Class::*method_ptr) -> bool
-{
-	return method_ptr;
-}
-
-template <class Function>
-auto not_null(yacppdic::Factory<Function> const &factory) -> bool
-{
-	return !!factory;
-}
-
-namespace yacppdic
-{
-
-template <class Return>
-// NOLINTNEXTLINE(readability-identifier-naming)
-struct maybe_derive_from_unary_function
-{
-};
-
-template <class Return, class Arg>
-struct maybe_derive_from_unary_function<Return(Arg)>
-	: public std::unary_function<Arg, Return>
-{
-};
-
-template <class Return>
-// NOLINTNEXTLINE(readability-identifier-naming)
-struct maybe_derive_from_binary_function
-{
-};
-
-template <class Return, class ArgOne, class ArgTwo>
-struct maybe_derive_from_binary_function<Return(ArgOne, ArgTwo)>
-	: public std::binary_function<ArgOne, ArgTwo, Return>
-{
-};
-
 template <typename Function, typename Return, typename... Args>
 concept Callable =
 	!std::is_same_v<
@@ -80,9 +28,9 @@ concept Callable =
 	std::is_invocable_v<Function, Args...> &&
 	internal::IsCoreConvertibleV<std::invoke_result_t<Function, Args...>, Return>;
 
-template <class Return, class... Args>
-class Factory<Return(Args...)> : public maybe_derive_from_unary_function<Return(Args...)>,
-								 public maybe_derive_from_binary_function<Return(Args...)>
+template <typename Return, typename... Args>
+class Factory<Return(Args...)> : public MaybeDeriveFromUnaryFunction<Return(Args...)>,
+								 public MaybeDeriveFromBinaryFunction<Return(Args...)>
 {
 public:
 	using Result = Return;
@@ -91,35 +39,36 @@ public:
 
 	explicit Factory(std::nullptr_t) noexcept {}
 
-	Factory(const Factory &factory);
+	Factory(const Factory &factory) noexcept;
 
 	Factory(Factory &&factory) noexcept;
 
-	template <class Function>
+	template <typename Function>
 	requires Callable<Function, Return, Args...>
 	// NOLINTNEXTLINE(google-explicit-constructor)
-	Factory(Function function) : _functor(std::move(function))
-	{
-	}
+	Factory(Function function)
+	noexcept : _functor(std::move(function)) {}
 
-	auto operator=(const Factory &factory) = delete;
+	auto operator=(const Factory &factory) noexcept = delete;
 
 	auto operator=(Factory &&factory) noexcept -> Factory &;
 
 	auto operator=(std::nullptr_t) noexcept -> Factory &;
 
-	~Factory();
+	~Factory() noexcept = default;
 
 	explicit operator bool() const noexcept;
 
 	// deleted overloads close possible hole in the type system
-	template <class RhsReturn, class... RhsArgs>
-	auto operator==(const Factory<RhsReturn(RhsArgs...)> &) const -> bool = delete;
+	template <typename RhsReturn, typename... RhsArgs>
+	auto operator==(const Factory<RhsReturn(RhsArgs...)> &) const noexcept
+		-> bool = delete;
 
-	template <class RhsReturn, class... RhsArgs>
-	auto operator!=(const Factory<RhsReturn(RhsArgs...)> &) const -> bool = delete;
+	template <typename RhsReturn, typename... RhsArgs>
+	auto operator!=(const Factory<RhsReturn(RhsArgs...)> &) const noexcept
+		-> bool = delete;
 
-	auto operator()(Args... args) const -> Return;
+	auto operator()(Args... args) const noexcept -> Return;
 
 	[[nodiscard]] auto target_type() const noexcept -> const std::type_info &;
 
@@ -135,42 +84,42 @@ private:
 	ValFunctor _functor;
 };
 
-template <class Return, class... Args>
+template <typename Return, typename... Args>
 Factory(Return (*)(Args...)) -> Factory<Return(Args...)>;
 
 template <
-	class Function,
-	class Stripped = internal::StripSignatureT<decltype(&Function::operator())>>
+	typename Function,
+	typename Stripped = internal::StripSignatureT<decltype(&Function::operator())>>
 Factory(Function) -> Factory<Stripped>;
 
-template <class Return, class... Args>
+template <typename Return, typename... Args>
 inline auto operator==(const Factory<Return(Args...)> &factory, std::nullptr_t) noexcept
-	-> bool
-{
-	return !factory;
-}
+	-> bool;
 
-template <class Return, class... Args>
+template <typename Return, typename... Args>
 inline auto operator==(std::nullptr_t, const Factory<Return(Args...)> &factory) noexcept
-	-> bool
-{
-	return !factory;
-}
+	-> bool;
 
-template <class Return, class... Args>
+template <typename Return, typename... Args>
 inline auto operator!=(const Factory<Return(Args...)> &factory, std::nullptr_t) noexcept
-	-> bool
-{
-	return static_cast<bool>(factory);
-}
+	-> bool;
 
-template <class Return, class... Args>
+template <typename Return, typename... Args>
 inline auto operator!=(std::nullptr_t, const Factory<Return(Args...)> &factory) noexcept
-	-> bool
-{
-	return static_cast<bool>(factory);
-}
+	-> bool;
 
 } // namespace yacppdic
 
+template <typename Function>
+constexpr auto not_null(Function const & /*unused*/) -> bool;
+
+template <typename Function>
+constexpr auto not_null(Function *function_ptr) -> bool;
+
+template <typename Return, typename Class>
+constexpr auto not_null(Return Class::*method_ptr) -> bool;
+
+template <typename Function>
+constexpr auto not_null(yacppdic::Factory<Function> const &factory) -> bool;
+
 #include "yacppdic/detail/factory-impl.hpp"