media/utils/include/mediautils/InPlaceFunction.h - LeafOS-Project/android_frameworks_av - Gitiles

 /*
  * Copyright (C) 2022 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #pragma once

 #include <cstdlib>
 #include <functional>
 #include <memory>
 #include <type_traits>

 namespace android::mediautils {

 namespace detail {
 // Vtable interface for erased types
 template <typename Ret, typename... Args>
 struct ICallableTable {
     // Destroy the erased type
     void (*destroy)(void* storage) = nullptr;
     // Call the erased object
     Ret (*invoke)(void* storage, Args&&...) = nullptr;
     // **Note** the next two functions only copy object data, not the vptr
     // Copy the erased object to a new InPlaceFunction buffer
     void (*copy_to)(const void* storage, void* other) = nullptr;
     // Move the erased object to a new InPlaceFunction buffer
     void (*move_to)(void* storage, void* other) = nullptr;
 };
 }  // namespace detail

 // This class is an *almost* drop-in replacement for std::function which is guaranteed to never
 // allocate, and always holds the type erased functional object in an in-line small buffer of
 // templated size. If the object is too large to hold, the type will fail to instantiate.
 //
 // Some notable differences are:
 // - operator() is not const (unlike std::function where the call operator is
 // const even if the erased type is not const callable). This retains const
 // correctness by default. A workaround is keeping InPlaceFunction mutable.
 // - Moving from an InPlaceFunction leaves the object in a valid state (operator
 // bool remains true), similar to std::optional/std::variant.
 // Calls to the object are still defined (and are equivalent
 // to calling the underlying type after it has been moved from). To opt-out
 // (and/or ensure safety), clearing the object is recommended:
 //      func1 = std::move(func2); // func2 still valid (and moved-from) after this line
 //      func2 = nullptr; // calling func2 will now abort
 // - Unsafe implicit conversions of the return value to a reference type are
 // prohibited due to the risk of dangling references (some of this safety was
 // added to std::function in c++23). Only converting a reference to a reference to base class is
 // permitted:
 //      std::function<Base&()> = []() -> Derived& {...}
 // - Some (current libc++ implementation) implementations of std::function
 // incorrectly fail to handle returning non-moveable types which is valid given
 // mandatory copy elision.
 //
 // Additionally, the stored functional will use the typical rules of overload
 // resolution to disambiguate the correct call, except, the target class will
 // always be implicitly a non-const lvalue when called. If a different overload
 // is preferred, wrapping the target class in a lambda with explicit casts is
 // recommended (or using inheritance, mixins or CRTP). This avoids the
 // complexity of utilizing abonimable function types as template params.
 template <typename, size_t BufferSize = 32>
 class InPlaceFunction;
 // We partially specialize to match types which are spelled like functions
 template <typename Ret, typename... Args, size_t BufferSize>
 class InPlaceFunction<Ret(Args...), BufferSize> {
   public:
     // Storage Type Details
     static constexpr size_t Size = BufferSize;
     static constexpr size_t Alignment = alignof(std::max_align_t);
     using Buffer_t = std::aligned_storage_t<Size, Alignment>;
     template <typename T, size_t Other>
     friend class InPlaceFunction;

   private:
     // Callable which is used for empty InPlaceFunction objects (to match the
     // std::function interface).
     struct BadCallable {
         [[noreturn]] Ret operator()(Args...) { std::abort(); }
     };
     static_assert(std::is_trivially_destructible_v<BadCallable>);

     // Implementation of vtable interface for erased types.
     // Contains only static vtable instantiated once for each erased type and
     // static helpers.
     template <typename T>
     struct TableImpl {
         // T should be a decayed type
         static_assert(std::is_same_v<T, std::decay_t<T>>);

         // Helper functions to get an unerased reference to the type held in the
         // buffer. std::launder is required to avoid strict aliasing rules.
         // The cast is always defined, as a precondition for these calls is that
         // (exactly) a T was placement new constructed into the buffer.
         constexpr static T& getRef(void* storage) {
             return *std::launder(reinterpret_cast<T*>(storage));
         }

         constexpr static const T& getRef(const void* storage) {
             return *std::launder(reinterpret_cast<const T*>(storage));
         }

         // Constexpr implies inline
         constexpr static detail::ICallableTable<Ret, Args...> table = {
                 // Stateless lambdas are convertible to function ptrs
                 .destroy = [](void* storage) { getRef(storage).~T(); },
                 .invoke = [](void* storage, Args&&... args) -> Ret {
                     if constexpr (std::is_void_v<Ret>) {
                         std::invoke(getRef(storage), std::forward<Args>(args)...);
                     } else {
                         return std::invoke(getRef(storage), std::forward<Args>(args)...);
                     }
                 },
                 .copy_to = [](const void* storage,
                               void* other) { ::new (other) T(getRef(storage)); },
                 .move_to = [](void* storage,
                               void* other) { ::new (other) T(std::move(getRef(storage))); },
         };
     };

     // Check size/align requirements for the T in Buffer_t.
     template <typename T>
     static constexpr bool WillFit_v = sizeof(T) <= Size && alignof(T) <= Alignment;

     // Check size/align requirements for a function to function conversion
     template <typename T>
     static constexpr bool ConversionWillFit_v = (T::Size < Size) && (T::Alignment <= Alignment);

     template <typename T>
     struct IsInPlaceFunction : std::false_type {};

     template <size_t BufferSize_>
     struct IsInPlaceFunction<InPlaceFunction<Ret(Args...), BufferSize_>> : std::true_type {};

     template <typename T>
     static T BetterDeclval();
     template <typename T>
     static void CheckImplicitConversion(T);

     template <class T, class U, class = void>
     struct CanImplicitConvert : std::false_type {};

     // std::is_convertible/std::invokeable has a bug (in libc++) regarding
     // mandatory copy elision for non-moveable types. So, we roll our own.
     // https://github.com/llvm/llvm-project/issues/55346
     template <class From, class To>
     struct CanImplicitConvert<From, To,
                               decltype(CheckImplicitConversion<To>(BetterDeclval<From>()))>
         : std::true_type {};

     // Check if the provided type is a valid functional to be type-erased.
     // if constexpr utilized for short-circuit behavior
     template <typename T>
     static constexpr bool isValidFunctional() {
         using Target = std::decay_t<T>;
         if constexpr (IsInPlaceFunction<Target>::value || std::is_same_v<Target, std::nullptr_t>) {
             // Other overloads handle these cases
             return false;
         } else if constexpr (std::is_invocable_v<Target, Args...>) {
             // The target type is a callable (with some unknown return value)
             if constexpr (std::is_void_v<Ret>) {
                 // Any return value can be dropped to model a void returning
                 // function.
                 return WillFit_v<Target>;
             } else {
                 using RawRet = std::invoke_result_t<Target, Args...>;
                 if constexpr (CanImplicitConvert<RawRet, Ret>::value) {
                     if constexpr (std::is_reference_v<Ret>) {
                         // If the return type is a reference, in order to
                         // avoid dangling references, we only permit functionals
                         // which return a reference to the exact type, or a base
                         // type.
                         if constexpr (std::is_reference_v<RawRet> &&
                                       (std::is_same_v<std::decay_t<Ret>, std::decay_t<RawRet>> ||
                                        std::is_base_of_v<std::decay_t<Ret>,
                                                          std::decay_t<RawRet>>)) {
                             return WillFit_v<Target>;
                         }
                         return false;
                     }
                     return WillFit_v<Target>;
                 }
                 // If we can't convert the raw return type, the functional is invalid.
                 return false;
             }
         }
         return false;
     }

     template <typename T>
     static constexpr bool IsValidFunctional_v = isValidFunctional<T>();
     // Check if the type is a strictly smaller sized InPlaceFunction
     template <typename T>
     static constexpr bool isConvertibleFunc() {
         using Target = std::decay_t<T>;
         if constexpr (IsInPlaceFunction<Target>::value) {
             return ConversionWillFit_v<Target>;
         }
         return false;
     }

     template <typename T>
     static constexpr bool IsConvertibleFunc_v = isConvertibleFunc<T>();

     // Members below
     // This must come first for alignment
     Buffer_t storage_;
     const detail::ICallableTable<Ret, Args...>* vptr_;

     constexpr void copy_to(InPlaceFunction& other) const {
         vptr_->copy_to(std::addressof(storage_), std::addressof(other.storage_));
         other.vptr_ = vptr_;
     }

     constexpr void move_to(InPlaceFunction& other) {
         vptr_->move_to(std::addressof(storage_), std::addressof(other.storage_));
         other.vptr_ = vptr_;
     }

     constexpr void destroy() { vptr_->destroy(std::addressof(storage_)); }

     template <typename T, typename Target = std::decay_t<T>>
     constexpr void genericInit(T&& t) {
         vptr_ = &TableImpl<Target>::table;
         ::new (std::addressof(storage_)) Target(std::forward<T>(t));
     }

     template <typename T, typename Target = std::decay_t<T>>
     constexpr void convertingInit(T&& smallerFunc) {
         // Redundant, but just in-case
         static_assert(Target::Size < Size && Target::Alignment <= Alignment);
         if constexpr (std::is_lvalue_reference_v<T>) {
             smallerFunc.vptr_->copy_to(std::addressof(smallerFunc.storage_),
                                        std::addressof(storage_));
         } else {
             smallerFunc.vptr_->move_to(std::addressof(smallerFunc.storage_),
                                        std::addressof(storage_));
         }
         vptr_ = smallerFunc.vptr_;
     }

   public:
     // Public interface
     template <typename T, std::enable_if_t<IsValidFunctional_v<T>>* = nullptr>
     constexpr InPlaceFunction(T&& t) {
         genericInit(std::forward<T>(t));
     }

     // Conversion from smaller functions.
     template <typename T, std::enable_if_t<IsConvertibleFunc_v<T>>* = nullptr>
     constexpr InPlaceFunction(T&& t) {
         convertingInit(std::forward<T>(t));
     }

     constexpr InPlaceFunction(const InPlaceFunction& other) { other.copy_to(*this); }

     constexpr InPlaceFunction(InPlaceFunction&& other) { other.move_to(*this); }

     // Making functions default constructible has pros and cons, we will align
     // with the standard
     constexpr InPlaceFunction() : InPlaceFunction(BadCallable{}) {}

     constexpr InPlaceFunction(std::nullptr_t) : InPlaceFunction(BadCallable{}) {}

 #if __cplusplus >= 202002L
     constexpr ~InPlaceFunction() {
 #else
     ~InPlaceFunction() {
 #endif
         destroy();
     }

     // The std::function call operator is marked const, but this violates const
     // correctness. We deviate from the standard and do not mark the operator as
     // const. Collections of InPlaceFunctions should probably be mutable.
     constexpr Ret operator()(Args... args) {
         if constexpr (std::is_void_v<Ret>) {
             vptr_->invoke(std::addressof(storage_), std::forward<Args>(args)...);
         } else {
             return vptr_->invoke(std::addressof(storage_), std::forward<Args>(args)...);
         }
     }

     constexpr InPlaceFunction& operator=(const InPlaceFunction& other) {
         if (std::addressof(other) == this) return *this;
         destroy();
         other.copy_to(*this);
         return *this;
     }

     constexpr InPlaceFunction& operator=(InPlaceFunction&& other) {
         if (std::addressof(other) == this) return *this;
         destroy();
         other.move_to(*this);
         return *this;
     }

     template <typename T, std::enable_if_t<IsValidFunctional_v<T>>* = nullptr>
     constexpr InPlaceFunction& operator=(T&& t) {
         // We can't assign to ourselves, since T is a different type
         destroy();
         genericInit(std::forward<T>(t));
         return *this;
     }

     // Explicitly defining this function saves a move/dtor
     template <typename T, std::enable_if_t<IsConvertibleFunc_v<T>>* = nullptr>
     constexpr InPlaceFunction& operator=(T&& t) {
         // We can't assign to ourselves, since T is different type
         destroy();
         convertingInit(std::forward<T>(t));
         return *this;
     }

     constexpr InPlaceFunction& operator=(std::nullptr_t) { return operator=(BadCallable{}); }

     // Moved from InPlaceFunctions are still considered valid (similar to
     // std::optional). If using std::move on a function object explicitly, it is
     // recommended that the object is reset using nullptr.
     constexpr explicit operator bool() const { return vptr_ != &TableImpl<BadCallable>::table; }

     constexpr void swap(InPlaceFunction& other) {
         if (std::addressof(other) == this) return;
         InPlaceFunction tmp{std::move(other)};
         other.destroy();
         move_to(other);
         destroy();
         tmp.move_to(*this);
     }

     friend constexpr void swap(InPlaceFunction& lhs, InPlaceFunction& rhs) { lhs.swap(rhs); }
 };

 }  // namespace android::mediautils
	/*
	* Copyright (C) 2022 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#pragma once

	#include <cstdlib>
	#include <functional>
	#include <memory>
	#include <type_traits>

	namespace android::mediautils {

	namespace detail {
	// Vtable interface for erased types
	template <typename Ret, typename... Args>
	struct ICallableTable {
	// Destroy the erased type
	void (destroy)(void storage) = nullptr;
	// Call the erased object
	Ret (invoke)(void storage, Args&&...) = nullptr;
	// Note the next two functions only copy object data, not the vptr
	// Copy the erased object to a new InPlaceFunction buffer
	void (copy_to)(const void storage, void* other) = nullptr;
	// Move the erased object to a new InPlaceFunction buffer
	void (move_to)(void storage, void* other) = nullptr;
	};
	} // namespace detail

	// This class is an almost drop-in replacement for std::function which is guaranteed to never
	// allocate, and always holds the type erased functional object in an in-line small buffer of
	// templated size. If the object is too large to hold, the type will fail to instantiate.
	//
	// Some notable differences are:
	// - operator() is not const (unlike std::function where the call operator is
	// const even if the erased type is not const callable). This retains const
	// correctness by default. A workaround is keeping InPlaceFunction mutable.
	// - Moving from an InPlaceFunction leaves the object in a valid state (operator
	// bool remains true), similar to std::optional/std::variant.
	// Calls to the object are still defined (and are equivalent
	// to calling the underlying type after it has been moved from). To opt-out
	// (and/or ensure safety), clearing the object is recommended:
	// func1 = std::move(func2); // func2 still valid (and moved-from) after this line
	// func2 = nullptr; // calling func2 will now abort
	// - Unsafe implicit conversions of the return value to a reference type are
	// prohibited due to the risk of dangling references (some of this safety was
	// added to std::function in c++23). Only converting a reference to a reference to base class is
	// permitted:
	// std::function<Base&()> = []() -> Derived& {...}
	// - Some (current libc++ implementation) implementations of std::function
	// incorrectly fail to handle returning non-moveable types which is valid given
	// mandatory copy elision.
	//
	// Additionally, the stored functional will use the typical rules of overload
	// resolution to disambiguate the correct call, except, the target class will
	// always be implicitly a non-const lvalue when called. If a different overload
	// is preferred, wrapping the target class in a lambda with explicit casts is
	// recommended (or using inheritance, mixins or CRTP). This avoids the
	// complexity of utilizing abonimable function types as template params.
	template <typename, size_t BufferSize = 32>
	class InPlaceFunction;
	// We partially specialize to match types which are spelled like functions
	template <typename Ret, typename... Args, size_t BufferSize>
	class InPlaceFunction<Ret(Args...), BufferSize> {
	public:
	// Storage Type Details
	static constexpr size_t Size = BufferSize;
	static constexpr size_t Alignment = alignof(std::max_align_t);
	using Buffer_t = std::aligned_storage_t<Size, Alignment>;
	template <typename T, size_t Other>
	friend class InPlaceFunction;

	private:
	// Callable which is used for empty InPlaceFunction objects (to match the
	// std::function interface).
	struct BadCallable {
	[[noreturn]] Ret operator()(Args...) { std::abort(); }
	};
	static_assert(std::is_trivially_destructible_v<BadCallable>);

	// Implementation of vtable interface for erased types.
	// Contains only static vtable instantiated once for each erased type and
	// static helpers.
	template <typename T>
	struct TableImpl {
	// T should be a decayed type
	static_assert(std::is_same_v<T, std::decay_t<T>>);

	// Helper functions to get an unerased reference to the type held in the
	// buffer. std::launder is required to avoid strict aliasing rules.
	// The cast is always defined, as a precondition for these calls is that
	// (exactly) a T was placement new constructed into the buffer.
	constexpr static T& getRef(void* storage) {
	return std::launder(reinterpret_cast<T>(storage));
	}

	constexpr static const T& getRef(const void* storage) {
	return std::launder(reinterpret_cast<const T>(storage));
	}

	// Constexpr implies inline
	constexpr static detail::ICallableTable<Ret, Args...> table = {
	// Stateless lambdas are convertible to function ptrs
	.destroy = [](void* storage) { getRef(storage).~T(); },
	.invoke = [](void* storage, Args&&... args) -> Ret {
	if constexpr (std::is_void_v<Ret>) {
	std::invoke(getRef(storage), std::forward<Args>(args)...);
	} else {
	return std::invoke(getRef(storage), std::forward<Args>(args)...);
	}
	},
	.copy_to = [](const void* storage,
	void* other) { ::new (other) T(getRef(storage)); },
	.move_to = [](void* storage,
	void* other) { ::new (other) T(std::move(getRef(storage))); },
	};
	};

	// Check size/align requirements for the T in Buffer_t.
	template <typename T>
	static constexpr bool WillFit_v = sizeof(T) <= Size && alignof(T) <= Alignment;

	// Check size/align requirements for a function to function conversion
	template <typename T>
	static constexpr bool ConversionWillFit_v = (T::Size < Size) && (T::Alignment <= Alignment);

	template <typename T>
	struct IsInPlaceFunction : std::false_type {};

	template <size_t BufferSize_>
	struct IsInPlaceFunction<InPlaceFunction<Ret(Args...), BufferSize_>> : std::true_type {};

	template <typename T>
	static T BetterDeclval();
	template <typename T>
	static void CheckImplicitConversion(T);

	template <class T, class U, class = void>
	struct CanImplicitConvert : std::false_type {};

	// std::is_convertible/std::invokeable has a bug (in libc++) regarding
	// mandatory copy elision for non-moveable types. So, we roll our own.
	// https://github.com/llvm/llvm-project/issues/55346
	template <class From, class To>
	struct CanImplicitConvert<From, To,
	decltype(CheckImplicitConversion<To>(BetterDeclval<From>()))>
	: std::true_type {};

	// Check if the provided type is a valid functional to be type-erased.
	// if constexpr utilized for short-circuit behavior
	template <typename T>
	static constexpr bool isValidFunctional() {
	using Target = std::decay_t<T>;
	if constexpr (IsInPlaceFunction<Target>::value \|\| std::is_same_v<Target, std::nullptr_t>) {
	// Other overloads handle these cases
	return false;
	} else if constexpr (std::is_invocable_v<Target, Args...>) {
	// The target type is a callable (with some unknown return value)
	if constexpr (std::is_void_v<Ret>) {
	// Any return value can be dropped to model a void returning
	// function.
	return WillFit_v<Target>;
	} else {
	using RawRet = std::invoke_result_t<Target, Args...>;
	if constexpr (CanImplicitConvert<RawRet, Ret>::value) {
	if constexpr (std::is_reference_v<Ret>) {
	// If the return type is a reference, in order to
	// avoid dangling references, we only permit functionals
	// which return a reference to the exact type, or a base
	// type.
	if constexpr (std::is_reference_v<RawRet> &&
	(std::is_same_v<std::decay_t<Ret>, std::decay_t<RawRet>> \|\|
	std::is_base_of_v<std::decay_t<Ret>,
	std::decay_t<RawRet>>)) {
	return WillFit_v<Target>;
	}
	return false;
	}
	return WillFit_v<Target>;
	}
	// If we can't convert the raw return type, the functional is invalid.
	return false;
	}
	}
	return false;
	}

	template <typename T>
	static constexpr bool IsValidFunctional_v = isValidFunctional<T>();
	// Check if the type is a strictly smaller sized InPlaceFunction
	template <typename T>
	static constexpr bool isConvertibleFunc() {
	using Target = std::decay_t<T>;
	if constexpr (IsInPlaceFunction<Target>::value) {
	return ConversionWillFit_v<Target>;
	}
	return false;
	}

	template <typename T>
	static constexpr bool IsConvertibleFunc_v = isConvertibleFunc<T>();

	// Members below
	// This must come first for alignment
	Buffer_t storage_;
	const detail::ICallableTable<Ret, Args...>* vptr_;

	constexpr void copy_to(InPlaceFunction& other) const {
	vptr_->copy_to(std::addressof(storage_), std::addressof(other.storage_));
	other.vptr_ = vptr_;
	}

	constexpr void move_to(InPlaceFunction& other) {
	vptr_->move_to(std::addressof(storage_), std::addressof(other.storage_));
	other.vptr_ = vptr_;
	}

	constexpr void destroy() { vptr_->destroy(std::addressof(storage_)); }

	template <typename T, typename Target = std::decay_t<T>>
	constexpr void genericInit(T&& t) {
	vptr_ = &TableImpl<Target>::table;
	::new (std::addressof(storage_)) Target(std::forward<T>(t));
	}

	template <typename T, typename Target = std::decay_t<T>>
	constexpr void convertingInit(T&& smallerFunc) {
	// Redundant, but just in-case
	static_assert(Target::Size < Size && Target::Alignment <= Alignment);
	if constexpr (std::is_lvalue_reference_v<T>) {
	smallerFunc.vptr_->copy_to(std::addressof(smallerFunc.storage_),
	std::addressof(storage_));
	} else {
	smallerFunc.vptr_->move_to(std::addressof(smallerFunc.storage_),
	std::addressof(storage_));
	}
	vptr_ = smallerFunc.vptr_;
	}

	public:
	// Public interface
	template <typename T, std::enable_if_t<IsValidFunctional_v<T>>* = nullptr>
	constexpr InPlaceFunction(T&& t) {
	genericInit(std::forward<T>(t));
	}

	// Conversion from smaller functions.
	template <typename T, std::enable_if_t<IsConvertibleFunc_v<T>>* = nullptr>
	constexpr InPlaceFunction(T&& t) {
	convertingInit(std::forward<T>(t));
	}

	constexpr InPlaceFunction(const InPlaceFunction& other) { other.copy_to(*this); }

	constexpr InPlaceFunction(InPlaceFunction&& other) { other.move_to(*this); }

	// Making functions default constructible has pros and cons, we will align
	// with the standard
	constexpr InPlaceFunction() : InPlaceFunction(BadCallable{}) {}

	constexpr InPlaceFunction(std::nullptr_t) : InPlaceFunction(BadCallable{}) {}

	#if __cplusplus >= 202002L
	constexpr ~InPlaceFunction() {
	#else
	~InPlaceFunction() {
	#endif
	destroy();
	}

	// The std::function call operator is marked const, but this violates const
	// correctness. We deviate from the standard and do not mark the operator as
	// const. Collections of InPlaceFunctions should probably be mutable.
	constexpr Ret operator()(Args... args) {
	if constexpr (std::is_void_v<Ret>) {
	vptr_->invoke(std::addressof(storage_), std::forward<Args>(args)...);
	} else {
	return vptr_->invoke(std::addressof(storage_), std::forward<Args>(args)...);
	}
	}

	constexpr InPlaceFunction& operator=(const InPlaceFunction& other) {
	if (std::addressof(other) == this) return *this;
	destroy();
	other.copy_to(*this);
	return *this;
	}

	constexpr InPlaceFunction& operator=(InPlaceFunction&& other) {
	if (std::addressof(other) == this) return *this;
	destroy();
	other.move_to(*this);
	return *this;
	}

	template <typename T, std::enable_if_t<IsValidFunctional_v<T>>* = nullptr>
	constexpr InPlaceFunction& operator=(T&& t) {
	// We can't assign to ourselves, since T is a different type
	destroy();
	genericInit(std::forward<T>(t));
	return *this;
	}

	// Explicitly defining this function saves a move/dtor
	template <typename T, std::enable_if_t<IsConvertibleFunc_v<T>>* = nullptr>
	constexpr InPlaceFunction& operator=(T&& t) {
	// We can't assign to ourselves, since T is different type
	destroy();
	convertingInit(std::forward<T>(t));
	return *this;
	}

	constexpr InPlaceFunction& operator=(std::nullptr_t) { return operator=(BadCallable{}); }

	// Moved from InPlaceFunctions are still considered valid (similar to
	// std::optional). If using std::move on a function object explicitly, it is
	// recommended that the object is reset using nullptr.
	constexpr explicit operator bool() const { return vptr_ != &TableImpl<BadCallable>::table; }

	constexpr void swap(InPlaceFunction& other) {
	if (std::addressof(other) == this) return;
	InPlaceFunction tmp{std::move(other)};
	other.destroy();
	move_to(other);
	destroy();
	tmp.move_to(*this);
	}

	friend constexpr void swap(InPlaceFunction& lhs, InPlaceFunction& rhs) { lhs.swap(rhs); }
	};

	} // namespace android::mediautils