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155 lines
3.6 KiB
C++
155 lines
3.6 KiB
C++
/*=============================================================================
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Copyright (c) 2015 Paul Fultz II
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repeat.h
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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==============================================================================*/
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#ifndef FIT_GUARD_REPEAT_H
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#define FIT_GUARD_REPEAT_H
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/// repeat
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/// ======
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///
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/// Description
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/// -----------
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///
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/// The `repeat` function decorator will repeatedly apply a function a given
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/// number of times.
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///
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///
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/// Synopsis
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/// --------
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///
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/// template<class Integral>
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/// constexpr repeat_adaptor<Integral> repeat(Integral);
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///
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/// Requirements
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/// ------------
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///
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/// Integral must be:
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///
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/// * Integral
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///
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/// Or:
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///
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/// * IntegralConstant
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///
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/// Example
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/// -------
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///
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/// #include <fit.hpp>
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/// #include <cassert>
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///
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/// struct increment
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/// {
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/// template<class T>
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/// constexpr T operator()(T x) const
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/// {
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/// return x + 1;
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/// }
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/// };
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///
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/// int main() {
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/// auto increment_by_5 = fit::repeat(std::integral_constant<int, 5>())(increment());
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/// assert(increment_by_5(1) == 6);
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/// }
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///
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#include <fit/always.hpp>
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#include <fit/detail/delegate.hpp>
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#include <fit/detail/result_of.hpp>
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#include <fit/detail/move.hpp>
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#include <fit/detail/static_const_var.hpp>
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#include <fit/decorate.hpp>
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#include <fit/conditional.hpp>
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#include <fit/detail/recursive_constexpr_depth.hpp>
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namespace fit { namespace detail {
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template<int N>
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struct repeater
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{
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template<class F, class... Ts>
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constexpr FIT_SFINAE_RESULT(repeater<N-1>, id_<const F&>, result_of<const F&, id_<Ts>...>)
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operator()(const F& f, Ts&&... xs) const FIT_SFINAE_RETURNS
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(
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repeater<N-1>()(f, f(FIT_FORWARD(Ts)(xs)...))
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);
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};
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template<>
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struct repeater<0>
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{
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template<class F, class T>
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constexpr T operator()(const F&, T&& x) const
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FIT_RETURNS_DEDUCE_NOEXCEPT(T(x))
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{
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return x;
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}
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};
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struct repeat_constant_decorator
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{
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template<class Integral, class F, class... Ts>
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constexpr auto operator()(Integral, const F& f, Ts&&... xs) const FIT_RETURNS
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(
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detail::repeater<Integral::type::value>()
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(
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f,
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FIT_FORWARD(Ts)(xs)...
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)
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);
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};
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template<int Depth>
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struct repeat_integral_decorator
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{
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template<class Integral, class F, class T, class... Ts, class Self=repeat_integral_decorator<Depth-1>>
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constexpr auto operator()(Integral n, const F& f, T&& x, Ts&&... xs) const FIT_RETURNS
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(
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(n) ?
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Self()(n-1, f, f(FIT_FORWARD(T)(x), FIT_FORWARD(Ts)(xs)...)) :
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FIT_FORWARD(T)(x)
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);
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};
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template<>
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struct repeat_integral_decorator<0>
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{
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template<class Integral, class F, class T, class Self=repeat_integral_decorator<0>>
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#if FIT_HAS_RELAXED_CONSTEXPR
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constexpr
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#endif
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auto operator()(Integral n, const F& f, T x) const
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FIT_RETURNS_DEDUCE_NOEXCEPT((n--, f(FIT_FORWARD(T)(x))))
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-> decltype(f(FIT_FORWARD(T)(x)))
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{
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while(n > 0)
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{
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n--;
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x = f(FIT_FORWARD(T)(x));
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}
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return x;
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}
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// TODO: Add overload for lvalue
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};
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}
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#if FIT_HAS_RELAXED_CONSTEXPR
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#define FIT_REPEAT_CONSTEXPR_DEPTH 1
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#else
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#define FIT_REPEAT_CONSTEXPR_DEPTH FIT_RECURSIVE_CONSTEXPR_DEPTH
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#endif
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FIT_DECLARE_STATIC_VAR(repeat, decorate_adaptor<
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fit::conditional_adaptor<
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detail::repeat_constant_decorator,
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detail::repeat_integral_decorator<FIT_REPEAT_CONSTEXPR_DEPTH>
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>>);
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} // namespace fit
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#endif
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