/*=============================================================================
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Copyright (c) 2014 Paul Fultz II
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static.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_STATIC_H
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#define BOOST_HOF_GUARD_FUNCTION_STATIC_H
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/// static
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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 `static_` adaptor is a static function adaptor that allows any
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/// default-constructible function object to be static-initialized. Functions
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/// initialized by `static_` cannot be used in `constexpr` functions. If the
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/// function needs to be statically initialized and called in a `constexpr`
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/// context, then a `constexpr` constructor needs to be used rather than
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/// `static_`.
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///
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/// Synopsis
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/// --------
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///
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/// template<class F>
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/// class static_;
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///
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/// Requirements
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/// ------------
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///
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/// F must be:
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///
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/// * [ConstFunctionObject](ConstFunctionObject)
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/// * DefaultConstructible
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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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/// using namespace boost::hof;
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///
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/// // In C++ this class can't be static-initialized, because of the non-
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/// // trivial default constructor.
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/// struct times_function
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/// {
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/// double factor;
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/// times_function() : factor(2)
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/// {}
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/// template<class T>
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/// T operator()(T x) const
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/// {
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/// return x*factor;
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/// }
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/// };
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///
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/// static constexpr static_<times_function> times2 = {};
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///
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/// int main() {
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/// assert(6 == times2(3));
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/// }
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///
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#include <boost/hof/detail/result_of.hpp>
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#include <boost/hof/reveal.hpp>
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namespace boost { namespace hof {
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template<class F>
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struct static_
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{
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struct failure
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: failure_for<F>
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{};
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const F& base_function() const
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BOOST_HOF_NOEXCEPT_CONSTRUCTIBLE(F)
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{
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static F f;
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return f;
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}
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BOOST_HOF_RETURNS_CLASS(static_);
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template<class... Ts>
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BOOST_HOF_SFINAE_RESULT(F, id_<Ts>...)
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operator()(Ts && ... xs) const
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BOOST_HOF_SFINAE_RETURNS(BOOST_HOF_CONST_THIS->base_function()(BOOST_HOF_FORWARD(Ts)(xs)...));
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};
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}} // namespace boost::hof
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#endif
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