utilities.hh
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Created: Wed, May 29, 11:33

utilities.hh
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	/**
	* @file utilities.hh
	*
	* @author Till Junge <till.junge@epfl.ch>
	*
	* @date 17 Nov 2017
	*
	* @brief additions to the standard name space to anticipate C++17 features
	*
	* Copyright © 2017 Till Junge
	*
	* µSpectre is free software; you can redistribute it and/or
	* modify it under the terms of the GNU Lesser General Public License as
	* published by the Free Software Foundation, either version 3, or (at
	* your option) any later version.
	*
	* µSpectre is distributed in the hope that it will be useful, but
	* WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* General Public License for more details.
	*
	* You should have received a copy of the GNU Lesser General Public License
	* along with µSpectre; see the file COPYING. If not, write to the
	* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
	* * Boston, MA 02111-1307, USA.
	*
	* Additional permission under GNU GPL version 3 section 7
	*
	* If you modify this Program, or any covered work, by linking or combining it
	* with proprietary FFT implementations or numerical libraries, containing parts
	* covered by the terms of those libraries' licenses, the licensors of this
	* Program grant you additional permission to convey the resulting work.
	*/

	#ifndef SRC_COMMON_UTILITIES_HH_
	#define SRC_COMMON_UTILITIES_HH_

	#include <tuple>

	#ifdef NO_EXPERIMENTAL
	#include <boost/optional.hpp>
	#else
	#include <experimental/optional>
	#endif

	namespace std_replacement {

	namespace detail {
	template <class T> struct is_reference_wrapper : std::false_type {};
	template <class U>
	struct is_reference_wrapper<std::reference_wrapper<U>> : std::true_type {};

	//! from cppreference
	template <class Base, class T, class Derived, class... Args>
	auto INVOKE(T Base::*pmf, Derived &&ref, Args &&... args) noexcept(noexcept(
	(std::forward<Derived>(ref).*pmf)(std::forward<Args>(args)...)))
	-> std::enable_if_t<
	std::is_function<T>::value &&
	std::is_base_of<Base, std::decay_t<Derived>>::value,
	decltype((std::forward<Derived>(ref).*
	pmf)(std::forward<Args>(args)...))> {
	return (std::forward<Derived>(ref).*pmf)(std::forward<Args>(args)...);
	}

	//! from cppreference
	template <class Base, class T, class RefWrap, class... Args>
	auto INVOKE(T Base::*pmf, RefWrap &&ref, Args &&... args) noexcept(
	noexcept((ref.get().*pmf)(std::forward<Args>(args)...)))
	-> std::enable_if_t<
	std::is_function<T>::value &&
	is_reference_wrapper<std::decay_t<RefWrap>>::value,
	decltype((ref.get().*pmf)(std::forward<Args>(args)...))> {
	return (ref.get().*pmf)(std::forward<Args>(args)...);
	}

	//! from cppreference
	template <class Base, class T, class Pointer, class... Args>
	auto INVOKE(T Base::*pmf, Pointer &&ptr, Args &&... args) noexcept(noexcept(
	((std::forward<Pointer>(ptr)).pmf)(std::forward<Args>(args)...)))
	-> std::enable_if_t<
	std::is_function<T>::value &&
	!is_reference_wrapper<std::decay_t<Pointer>>::value &&
	!std::is_base_of<Base, std::decay_t<Pointer>>::value,
	decltype(((std::forward<Pointer>(ptr)).
	pmf)(std::forward<Args>(args)...))> {
	return ((std::forward<Pointer>(ptr)).pmf)(std::forward<Args>(args)...);
	}

	//! from cppreference
	template <class Base, class T, class Derived>
	auto
	INVOKE(T Base::*pmd,
	Derived &&ref) noexcept(noexcept(std::forward<Derived>(ref).*pmd))
	-> std::enable_if_t<
	!std::is_function<T>::value &&
	std::is_base_of<Base, std::decay_t<Derived>>::value,
	decltype(std::forward<Derived>(ref).*pmd)> {
	return std::forward<Derived>(ref).*pmd;
	}

	//! from cppreference
	template <class Base, class T, class RefWrap>
	auto INVOKE(T Base::pmd, RefWrap &&ref) noexcept(noexcept(ref.get().pmd))
	-> std::enable_if_t<
	!std::is_function<T>::value &&
	is_reference_wrapper<std::decay_t<RefWrap>>::value,
	decltype(ref.get().*pmd)> {
	return ref.get().*pmd;
	}

	//! from cppreference
	template <class Base, class T, class Pointer>
	auto
	INVOKE(T Base::*pmd,
	Pointer &&ptr) noexcept(noexcept((std::forward<Pointer>(ptr)).pmd))
	-> std::enable_if_t<
	!std::is_function<T>::value &&
	!is_reference_wrapper<std::decay_t<Pointer>>::value &&
	!std::is_base_of<Base, std::decay_t<Pointer>>::value,
	decltype((std::forward<Pointer>(ptr)).pmd)> {
	return (std::forward<Pointer>(ptr)).pmd;
	}

	//! from cppreference
	template <class F, class... Args>
	auto INVOKE(F &&f, Args &&... args) noexcept(
	noexcept(std::forward<F>(f)(std::forward<Args>(args)...)))
	-> std::enable_if_t<
	!std::is_member_pointer<std::decay_t<F>>::value,
	decltype(std::forward<F>(f)(std::forward<Args>(args)...))> {
	return std::forward<F>(f)(std::forward<Args>(args)...);
	}
	} // namespace detail

	//! from cppreference
	template <class F, class... ArgTypes>
	auto invoke(F &&f, ArgTypes &&... args)
	// exception specification for QoI
	noexcept(noexcept(detail::INVOKE(std::forward<F>(f),
	std::forward<ArgTypes>(args)...)))
	-> decltype(detail::INVOKE(std::forward<F>(f),
	std::forward<ArgTypes>(args)...)) {
	return detail::INVOKE(std::forward<F>(f), std::forward<ArgTypes>(args)...);
	}

	namespace detail {
	//! from cppreference
	template <class F, class Tuple, std::size_t... I>
	constexpr decltype(auto) apply_impl(F &&f, Tuple &&t,
	std::index_sequence<I...>) {
	return std_replacement::invoke(std::forward<F>(f),
	std::get<I>(std::forward<Tuple>(t))...);
	}
	} // namespace detail

	//! from cppreference
	template <class F, class Tuple>
	constexpr decltype(auto) apply(F &&f, Tuple &&t) {
	return detail::apply_impl(
	std::forward<F>(f), std::forward<Tuple>(t),
	std::make_index_sequence<
	std::tuple_size<std::decay_t<Tuple>>::value>{});
	}

	} // namespace std_replacement

	namespace muSpectre {

	namespace internal {

	/**
	* helper struct template to compute the type of a tuple with a
	* given number of entries of the same type
	*/
	template <size_t size, typename T, typename... tail>
	struct tuple_array_helper {
	//! underlying tuple
	using type = typename tuple_array_helper<size - 1, T, T, tail...>::type;
	};

	/**
	* helper struct template to compute the type of a tuple with a
	* given number of entries of the same type
	*/
	template <typename T, typename... tail>
	struct tuple_array_helper<0, T, tail...> {
	//! underlying tuple
	using type = std::tuple<tail...>;
	};

	/**
	* helper struct for runtime index access to
	* tuples. RecursionLevel indicates how much more we can recurse
	* down
	*/
	template <class TupArr, size_t Index = 0,
	size_t RecursionLevel = TupArr::Size - 1>
	struct Accessor {
	using Stored_t = typename TupArr::Stored_t;

	inline static Stored_t get(const size_t &index, TupArr &container) {
	if (index == Index) {
	return std::get<Index>(container);
	} else {
	return Accessor<TupArr, Index + 1, RecursionLevel - 1>::get(
	index, container);
	}
	}
	inline static const Stored_t get(const size_t &index,
	const TupArr &container) {
	if (index == Index) {
	return std::get<Index>(container);
	} else {
	return Accessor<TupArr, Index + 1, RecursionLevel - 1>::get(
	index, container);
	}
	}
	};

	/**
	* specialisation for recursion end
	*/
	template <class TupArr, size_t Index> struct Accessor<TupArr, Index, 0> {
	using Stored_t = typename TupArr::Stored_t;

	inline static Stored_t get(const size_t &index, TupArr &container) {
	if (index == Index) {
	return std::get<Index>(container);
	} else {
	std::stringstream err{};
	err << "Index " << index << "is out of range.";
	throw std::runtime_error(err.str());
	}
	}

	inline static const Stored_t get(const size_t &index,
	const TupArr &container) {
	if (index == Index) {
	return std::get<Index>(container);
	} else {
	std::stringstream err{};
	err << "Index " << index << "is out of range.";
	throw std::runtime_error(err.str());
	}
	}
	};

	/**
	* helper struct that provides the tuple_array.
	*/
	template <typename T, size_t size> struct tuple_array_provider {
	//! tuple type that can be used (almost) like an `std::array`
	class type : public tuple_array_helper<size, T>::type {
	public:
	//! short-hand
	using Parent = typename tuple_array_helper<size, T>::type;
	using Stored_t = T;
	constexpr static size_t Size{size};

	//! constructor
	explicit inline type(Parent &&parent) : Parent{parent} {}

	//! element access
	T operator[](const size_t &index) {
	return Accessor<type>::get(index, *this);
	}

	//! element access
	const T operator[](const size_t &index) const {
	return Accessor<type>::get(index, *this);
	}

	protected:
	};
	};
	} // namespace internal

	/**
	* This is a convenience structure to create a tuple of `nb_elem`
	* entries of type `T`. It is named tuple_array, because it is
	* somewhat similar to an `std::array<T, nb_elem>`. The reason for
	* this structure is that the `std::array` is not allowed by the
	* standard to store references (8.3.2 References, paragraph 5:
	* "There shall be no references to references, no arrays of
	* references, and no pointers to references.") use this, if you
	* want to have a statically known number of references to store,
	* and you wish to do so efficiently.
	*/
	template <typename T, size_t nb_elem>
	using tuple_array = typename internal::tuple_array_provider<T, nb_elem>::type;

	using std_replacement::apply;

	/**
	* emulation `std::optional` (a C++17 feature)
	*/
	template <class T>
	#ifdef NO_EXPERIMENTAL
	using optional = typename boost::optional<T>;
	#else
	using optional = typename std::experimental::optional<T>;
	#endif

	} // namespace muSpectre

	#endif // SRC_COMMON_UTILITIES_HH_

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