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/*=============================================================================
Copyright (c) 2015 Paul Fultz II
repeat.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_REPEAT_H
#define BOOST_HOF_GUARD_REPEAT_H
/// repeat
/// ======
///
/// Description
/// -----------
///
/// The `repeat` function decorator will repeatedly apply a function a given
/// number of times.
///
///
/// Synopsis
/// --------
///
/// template<class Integral>
/// constexpr auto repeat(Integral);
///
/// Semantics
/// ---------
///
/// assert(repeat(std::integral_constant<int, 0>{})(f)(xs...) == f(xs...));
/// assert(repeat(std::integral_constant<int, 1>{})(f)(xs...) == f(f(xs...)));
/// assert(repeat(0)(f)(xs...) == f(xs...));
/// assert(repeat(1)(f)(xs...) == f(f(xs...)));
///
/// Requirements
/// ------------
///
/// Integral must be:
///
/// * Integral
///
/// Or:
///
/// * IntegralConstant
///
/// Example
/// -------
///
/// #include <boost/hof.hpp>
/// #include <cassert>
///
/// struct increment
/// {
/// template<class T>
/// constexpr T operator()(T x) const
/// {
/// return x + 1;
/// }
/// };
///
/// int main() {
/// auto increment_by_5 = boost::hof::repeat(std::integral_constant<int, 5>())(increment());
/// assert(increment_by_5(1) == 6);
/// }
///
#include <boost/hof/always.hpp>
#include <boost/hof/detail/delegate.hpp>
#include <boost/hof/detail/result_of.hpp>
#include <boost/hof/detail/move.hpp>
#include <boost/hof/detail/static_const_var.hpp>
#include <boost/hof/decorate.hpp>
#include <boost/hof/first_of.hpp>
#include <boost/hof/detail/recursive_constexpr_depth.hpp>
namespace boost { namespace hof { namespace detail {
template<int N>
struct repeater
{
template<class F, class... Ts>
constexpr BOOST_HOF_SFINAE_RESULT(repeater<N-1>, id_<const F&>, result_of<const F&, id_<Ts>...>)
operator()(const F& f, Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS
(
repeater<N-1>()(f, f(BOOST_HOF_FORWARD(Ts)(xs)...))
);
};
template<>
struct repeater<0>
{
template<class F, class T>
constexpr T operator()(const F&, T&& x) const
BOOST_HOF_RETURNS_DEDUCE_NOEXCEPT(T(x))
{
return x;
}
};
struct repeat_constant_decorator
{
template<class Integral, class F, class... Ts>
constexpr auto operator()(Integral, const F& f, Ts&&... xs) const BOOST_HOF_RETURNS
(
detail::repeater<Integral::type::value>()
(
f,
BOOST_HOF_FORWARD(Ts)(xs)...
)
);
};
template<int Depth>
struct repeat_integral_decorator
{
template<class Integral, class F, class T, class... Ts, class Self=repeat_integral_decorator<Depth-1>>
constexpr auto operator()(Integral n, const F& f, T&& x, Ts&&... xs) const BOOST_HOF_RETURNS
(
(n) ?
Self()(n-1, f, f(BOOST_HOF_FORWARD(T)(x), BOOST_HOF_FORWARD(Ts)(xs)...)) :
BOOST_HOF_FORWARD(T)(x)
);
};
template<>
struct repeat_integral_decorator<0>
{
template<class Integral, class F, class T, class Self=repeat_integral_decorator<0>>
#if BOOST_HOF_HAS_RELAXED_CONSTEXPR
constexpr
#endif
auto operator()(Integral n, const F& f, T x) const
BOOST_HOF_RETURNS_DEDUCE_NOEXCEPT((n--, f(BOOST_HOF_FORWARD(T)(x))))
-> decltype(f(BOOST_HOF_FORWARD(T)(x)))
{
while(n > 0)
{
n--;
x = f(BOOST_HOF_FORWARD(T)(x));
}
return x;
}
// TODO: Add overload for lvalue
};
}
#if BOOST_HOF_HAS_RELAXED_CONSTEXPR
#define BOOST_HOF_REPEAT_CONSTEXPR_DEPTH 1
#else
#define BOOST_HOF_REPEAT_CONSTEXPR_DEPTH BOOST_HOF_RECURSIVE_CONSTEXPR_DEPTH
#endif
BOOST_HOF_DECLARE_STATIC_VAR(repeat, decorate_adaptor<
boost::hof::first_of_adaptor<
detail::repeat_constant_decorator,
detail::repeat_integral_decorator<BOOST_HOF_REPEAT_CONSTEXPR_DEPTH>
>>);
}} // namespace boost::hof
#endif
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