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Diffstat (limited to 'boost/hof/repeat.hpp')
| -rw-r--r-- | boost/hof/repeat.hpp | 162 |
1 files changed, 162 insertions, 0 deletions
diff --git a/boost/hof/repeat.hpp b/boost/hof/repeat.hpp new file mode 100644 index 0000000000..e73e43ee06 --- /dev/null +++ b/boost/hof/repeat.hpp @@ -0,0 +1,162 @@ +/*============================================================================= + 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 |