Edit: /usr/include/boost/hof/fold.hpp (5000B)
/*=============================================================================
Copyright (c) 2015 Paul Fultz II
fold.h
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
==============================================================================*/
#ifndef BOOST_HOF_GUARD_FOLD_H
#define BOOST_HOF_GUARD_FOLD_H
/// fold
/// ========
///
/// Description
/// -----------
///
/// The `fold` function adaptor uses a binary function to apply a
/// [fold](https://en.wikipedia.org/wiki/Fold_%28higher-order_function%29)
/// operation to the arguments passed to the function. Additionally, an
/// optional initial state can be provided, otherwise the first argument is
/// used as the initial state.
///
/// The arguments to the binary function, take first the state and then the
/// argument.
///
/// Synopsis
/// --------
///
/// template
/// constexpr fold_adaptor fold(F f, State s);
///
/// template
/// constexpr fold_adaptor fold(F f);
///
/// Semantics
/// ---------
///
/// assert(fold(f, z)() == z);
/// assert(fold(f, z)(x, xs...) == fold(f, f(z, x))(xs...));
/// assert(fold(f)(x) == x);
/// assert(fold(f)(x, y, xs...) == fold(f)(f(x, y), xs...));
///
/// Requirements
/// ------------
///
/// State must be:
///
/// * CopyConstructible
///
/// F must be:
///
/// * [BinaryInvocable](BinaryInvocable)
/// * MoveConstructible
///
/// Example
/// -------
///
/// #include
/// #include
///
/// struct max_f
/// {
/// template
/// constexpr T operator()(T x, U y) const
/// {
/// return x > y ? x : y;
/// }
/// };
/// int main() {
/// assert(boost::hof::fold(max_f())(2, 3, 4, 5) == 5);
/// }
///
/// References
/// ----------
///
/// * [Fold](https://en.wikipedia.org/wiki/Fold_(higher-order_function))
/// * [Variadic sum]()
///
#include
#include
#include
#include
#include
#include
namespace boost { namespace hof { namespace detail {
struct v_fold
{
BOOST_HOF_RETURNS_CLASS(v_fold);
template
constexpr BOOST_HOF_SFINAE_MANUAL_RESULT(const v_fold&, id_, result_of, id_>, id_...)
operator()(const F& f, State&& state, T&& x, Ts&&... xs) const BOOST_HOF_SFINAE_MANUAL_RETURNS
(
(*BOOST_HOF_CONST_THIS)(f, f(BOOST_HOF_FORWARD(State)(state), BOOST_HOF_FORWARD(T)(x)), BOOST_HOF_FORWARD(Ts)(xs)...)
);
template
constexpr State operator()(const F&, State&& state) const noexcept
{
return BOOST_HOF_FORWARD(State)(state);
}
};
}
template
struct fold_adaptor
: detail::compressed_pair, State>
{
typedef detail::compressed_pair, State> base_type;
BOOST_HOF_INHERIT_CONSTRUCTOR(fold_adaptor, base_type)
template
constexpr const detail::callable_base& base_function(Ts&&... xs) const noexcept
{
return this->first(xs...);
}
template
constexpr State get_state(Ts&&... xs) const noexcept
{
return this->second(xs...);
}
BOOST_HOF_RETURNS_CLASS(fold_adaptor);
template
constexpr BOOST_HOF_SFINAE_RESULT(detail::v_fold, id_&>, id_, id_...)
operator()(Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS
(
detail::v_fold()(
BOOST_HOF_MANGLE_CAST(const detail::callable_base&)(BOOST_HOF_CONST_THIS->base_function(xs...)),
BOOST_HOF_MANGLE_CAST(State)(BOOST_HOF_CONST_THIS->get_state(xs...)),
BOOST_HOF_FORWARD(Ts)(xs)...
)
)
};
template
struct fold_adaptor
: detail::callable_base
{
BOOST_HOF_INHERIT_CONSTRUCTOR(fold_adaptor, detail::callable_base)
template
constexpr const detail::callable_base& base_function(Ts&&... xs) const noexcept
{
return boost::hof::always_ref(*this)(xs...);
}
BOOST_HOF_RETURNS_CLASS(fold_adaptor);
template
constexpr BOOST_HOF_SFINAE_RESULT(detail::v_fold, id_&>, id_...)
operator()(Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS
(
detail::v_fold()(
BOOST_HOF_MANGLE_CAST(const detail::callable_base&)(BOOST_HOF_CONST_THIS->base_function(xs...)),
BOOST_HOF_FORWARD(Ts)(xs)...
)
)
};
BOOST_HOF_DECLARE_STATIC_VAR(fold, detail::make);
}} // namespace boost::hof
#endif