/*=============================================================================
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Copyright (c) 2015 Paul Fultz II
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lift.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 BOOST_HOF_GUARD_FUNCTION_LIFT_H
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#define BOOST_HOF_GUARD_FUNCTION_LIFT_H
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/// BOOST_HOF_LIFT
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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 macros `BOOST_HOF_LIFT` and `BOOST_HOF_LIFT_CLASS` provide a lift operator that
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/// will wrap a template function in a function object so it can be passed to
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/// higher-order functions. The `BOOST_HOF_LIFT` macro will wrap the function using
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/// a generic lambda. As such, it will not preserve `constexpr`. The
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/// `BOOST_HOF_LIFT_CLASS` can be used to declare a class that will wrap function.
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/// This will preserve `constexpr` and it can be used on older compilers that
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/// don't support generic lambdas yet.
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///
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/// Limitation
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/// ----------
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///
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/// In C++14, `BOOST_HOF_LIFT` doesn't support `constexpr` due to using a generic
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/// lambda. Instead, `BOOST_HOF_LIFT_CLASS` can be used. In C++17, there is no such
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/// limitation.
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///
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/// Synopsis
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/// --------
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///
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/// // Wrap the function in a generic lambda
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/// #define BOOST_HOF_LIFT(...)
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///
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/// // Declare a class named `name` that will forward to the function
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/// #define BOOST_HOF_LIFT_CLASS(name, ...)
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///
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/// Example
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/// -------
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///
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/// #include <boost/hof.hpp>
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/// #include <cassert>
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/// #include <algorithm>
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///
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/// // Declare the class `max_f`
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/// BOOST_HOF_LIFT_CLASS(max_f, std::max);
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///
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/// int main() {
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/// auto my_max = BOOST_HOF_LIFT(std::max);
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/// assert(my_max(3, 4) == std::max(3, 4));
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/// assert(max_f()(3, 4) == std::max(3, 4));
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/// }
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///
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#include <boost/hof/detail/delegate.hpp>
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#include <boost/hof/returns.hpp>
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#include <boost/hof/lambda.hpp>
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#include <boost/hof/detail/forward.hpp>
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namespace boost { namespace hof { namespace detail {
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template<class F, class NoExcept>
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struct lift_noexcept : F
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{
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BOOST_HOF_INHERIT_CONSTRUCTOR(lift_noexcept, F);
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template<class... Ts>
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constexpr auto operator()(Ts&&... xs) const
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noexcept(decltype(std::declval<NoExcept>()(BOOST_HOF_FORWARD(Ts)(xs)...)){})
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-> decltype(std::declval<F>()(BOOST_HOF_FORWARD(Ts)(xs)...))
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{ return F(*this)(BOOST_HOF_FORWARD(Ts)(xs)...);}
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};
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template<class F, class NoExcept>
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constexpr lift_noexcept<F, NoExcept> make_lift_noexcept(F f, NoExcept)
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{
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return {f};
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}
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}
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}} // namespace boost::hof
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#define BOOST_HOF_LIFT_IS_NOEXCEPT(...) std::integral_constant<bool, noexcept(decltype(__VA_ARGS__)(__VA_ARGS__))>{}
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#if defined (_MSC_VER)
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#define BOOST_HOF_LIFT(...) (BOOST_HOF_STATIC_LAMBDA { BOOST_HOF_LIFT_CLASS(fit_local_lift_t, __VA_ARGS__); return fit_local_lift_t(); }())
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#elif defined (__clang__)
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#define BOOST_HOF_LIFT(...) (boost::hof::detail::make_lift_noexcept( \
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BOOST_HOF_STATIC_LAMBDA(auto&&... xs) \
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-> decltype((__VA_ARGS__)(BOOST_HOF_FORWARD(decltype(xs))(xs)...)) \
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{ return (__VA_ARGS__)(BOOST_HOF_FORWARD(decltype(xs))(xs)...); }, \
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BOOST_HOF_STATIC_LAMBDA(auto&&... xs) { return BOOST_HOF_LIFT_IS_NOEXCEPT((__VA_ARGS__)(BOOST_HOF_FORWARD(decltype(xs))(xs)...)); } \
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))
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#else
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#define BOOST_HOF_LIFT(...) (BOOST_HOF_STATIC_LAMBDA(auto&&... xs) BOOST_HOF_RETURNS((__VA_ARGS__)(BOOST_HOF_FORWARD(decltype(xs))(xs)...)))
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#endif
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#define BOOST_HOF_LIFT_CLASS(name, ...) \
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struct name \
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{ \
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template<class... Ts> \
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constexpr auto operator()(Ts&&... xs) const \
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BOOST_HOF_RETURNS((__VA_ARGS__)(BOOST_HOF_FORWARD(Ts)(xs)...)) \
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}
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#endif
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