feat():initial version

install/boost_1_75_0/include/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