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reverse_fold.hpp
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reverse_fold.hpp
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/*=============================================================================
Copyright (c) 2015 Paul Fultz II
reverse_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 FIT_GUARD_REVERSE_FOLD_H
#define FIT_GUARD_REVERSE_FOLD_H
/// reverse_fold
/// ========
///
/// Description
/// -----------
///
/// The `reverse_fold` function adaptor uses a binary function to apply a
/// reverse [fold]
/// (https://en.wikipedia.org/wiki/Fold_%28higher-order_function%29)(ie right
/// fold in functional programming terms) 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<class F, class State>
/// constexpr reverse_fold_adaptor<F, State> reverse_fold(F f, State s);
///
/// template<class F>
/// constexpr reverse_fold_adaptor<F> reverse_fold(F f);
///
/// Semantics
/// ---------
///
/// assert(reverse_fold(f, z)() == z);
/// assert(reverse_fold(f, z)(x, xs...) == f(reverse_fold(f, z)(xs...), x));
/// assert(reverse_fold(f)(x) == x);
/// assert(reverse_fold(f)(x, xs...) == f(reverse_fold(f)(xs...), x));
///
/// Requirements
/// ------------
///
/// State must be:
///
/// * CopyConstructible
///
/// F must be:
///
/// * [BinaryCallable](BinaryCallable)
/// * MoveConstructible
///
/// Example
/// -------
///
/// #include <fit.hpp>
/// #include <cassert>
///
/// struct max_f
/// {
/// template<class T, class U>
/// constexpr T operator()(T x, U y) const
/// {
/// return x > y ? x : y;
/// }
/// };
///
/// int main() {
/// assert(fit::reverse_fold(max_f())(2, 3, 4, 5) == 5);
/// }
///
/// References
/// ----------
///
/// * [Projections](Projections)
/// * [Variadic print](<Variadic print>)
///
#include <fit/detail/callable_base.hpp>
#include <fit/detail/delegate.hpp>
#include <fit/detail/compressed_pair.hpp>
#include <fit/detail/move.hpp>
#include <fit/detail/make.hpp>
#include <fit/detail/static_const_var.hpp>
namespace fit { namespace detail {
struct v_reverse_fold
{
FIT_RETURNS_CLASS(v_reverse_fold);
template<class F, class State, class T, class... Ts>
constexpr FIT_SFINAE_MANUAL_RESULT(const F&, result_of<const v_reverse_fold&, id_<const F&>, id_<State>, id_<Ts>...>, id_<T>)
operator()(const F& f, State&& state, T&& x, Ts&&... xs) const FIT_SFINAE_MANUAL_RETURNS
(
f((*FIT_CONST_THIS)(f, FIT_FORWARD(State)(state), FIT_FORWARD(Ts)(xs)...), FIT_FORWARD(T)(x))
);
template<class F, class State>
constexpr State operator()(const F&, State&& state) const noexcept
{
return FIT_FORWARD(State)(state);
}
};
}
template<class F, class State=void>
struct reverse_fold_adaptor
: detail::compressed_pair<detail::callable_base<F>, State>
{
typedef detail::compressed_pair<detail::callable_base<F>, State> base_type;
FIT_INHERIT_CONSTRUCTOR(reverse_fold_adaptor, base_type)
template<class... Ts>
constexpr const detail::callable_base<F>& base_function(Ts&&... xs) const noexcept
{
return this->first(xs...);
}
template<class... Ts>
constexpr State get_state(Ts&&... xs) const noexcept
{
return this->second(xs...);
}
FIT_RETURNS_CLASS(reverse_fold_adaptor);
template<class... Ts>
constexpr FIT_SFINAE_RESULT(detail::v_reverse_fold, id_<const detail::callable_base<F>&>, id_<State>, id_<Ts>...)
operator()(Ts&&... xs) const FIT_SFINAE_RETURNS
(
detail::v_reverse_fold()(
FIT_MANGLE_CAST(const detail::callable_base<F>&)(FIT_CONST_THIS->base_function(xs...)),
FIT_MANGLE_CAST(State)(FIT_CONST_THIS->get_state(xs...)),
FIT_FORWARD(Ts)(xs)...
)
)
};
template<class F>
struct reverse_fold_adaptor<F, void>
: detail::callable_base<F>
{
FIT_INHERIT_CONSTRUCTOR(reverse_fold_adaptor, detail::callable_base<F>)
template<class... Ts>
constexpr const detail::callable_base<F>& base_function(Ts&&... xs) const noexcept
{
return fit::always_ref(*this)(xs...);
}
FIT_RETURNS_CLASS(reverse_fold_adaptor);
template<class... Ts>
constexpr FIT_SFINAE_RESULT(detail::v_reverse_fold, id_<const detail::callable_base<F>&>, id_<Ts>...)
operator()(Ts&&... xs) const FIT_SFINAE_RETURNS
(
detail::v_reverse_fold()(
FIT_MANGLE_CAST(const detail::callable_base<F>&)(FIT_CONST_THIS->base_function(xs...)),
FIT_FORWARD(Ts)(xs)...
)
)
};
FIT_DECLARE_STATIC_VAR(reverse_fold, detail::make<reverse_fold_adaptor>);
} // namespace fit
#endif