143 lines
3.7 KiB
C++
143 lines
3.7 KiB
C++
/*=============================================================================
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Copyright (c) 2016 Paul Fultz II
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limit.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_LIMIT_H
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#define BOOST_HOF_GUARD_LIMIT_H
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/// limit
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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 `limit` function decorator annotates the function with the max number
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/// of parameters. The `limit_c` version can be used to give the max number
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/// directly(instead of relying on an integral constant). The parameter limit
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/// can be read by using the [`function_param_limit`](function_param_limit)
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/// trait. Using `limit` is useful to improve error reporting with partially
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/// evaluated functions.
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///
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/// Synopsis
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/// --------
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///
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/// template<class IntegralConstant>
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/// constexpr auto limit(IntegralConstant);
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///
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/// template<std::size_t N, class F>
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/// constexpr auto limit_c(F);
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///
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/// Requirements
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/// ------------
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///
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/// IntegralConstant must be:
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///
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/// * IntegralConstant
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///
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/// F must be:
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///
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/// * [ConstInvocable](ConstInvocable)
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/// * MoveConstructible
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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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/// struct sum_f
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/// {
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/// template<class T>
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/// int operator()(T x, T y) const
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/// {
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/// return x+y;
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/// }
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/// };
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/// BOOST_HOF_STATIC_FUNCTION(sum) = limit_c<2>(sum_f());
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///
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/// int main() {
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/// assert(3 == sum(1, 2));
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/// }
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///
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/// See Also
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/// --------
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///
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/// * [Partial function evaluation](<Partial function evaluation>)
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/// * [function_param_limit](function_param_limit)
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///
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#include <boost/hof/detail/callable_base.hpp>
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#include <boost/hof/detail/forward.hpp>
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#include <boost/hof/detail/delegate.hpp>
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#include <boost/hof/detail/move.hpp>
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#include <boost/hof/detail/static_const_var.hpp>
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#include <boost/hof/always.hpp>
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#include <boost/hof/function_param_limit.hpp>
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namespace boost { namespace hof {
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namespace detail {
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// TODO: Make this work with fit_rewritable1_tag
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template<std::size_t N, class F>
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struct limit_adaptor : detail::callable_base<F>
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{
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typedef std::integral_constant<std::size_t, N> fit_function_param_limit;
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BOOST_HOF_INHERIT_CONSTRUCTOR(limit_adaptor, detail::callable_base<F>)
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template<class... Ts>
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constexpr const detail::callable_base<F>& base_function(Ts&&... xs) const
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{
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return boost::hof::always_ref(*this)(xs...);
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}
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BOOST_HOF_RETURNS_CLASS(limit_adaptor);
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template<class... Ts, class=typename std::enable_if<(sizeof...(Ts) <= N)>::type>
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constexpr BOOST_HOF_SFINAE_RESULT(const detail::callable_base<F>&, id_<Ts>...)
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operator()(Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS
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(
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(BOOST_HOF_MANGLE_CAST(const detail::callable_base<F>&)(BOOST_HOF_CONST_THIS->base_function(xs...)))
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(BOOST_HOF_FORWARD(Ts)(xs)...)
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);
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};
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template<std::size_t N>
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struct make_limit_f
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{
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constexpr make_limit_f()
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{}
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template<class F>
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constexpr limit_adaptor<N, F> operator()(F f) const
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{
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return limit_adaptor<N, F>(static_cast<F&&>(f));
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}
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};
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struct limit_f
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{
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template<class IntegralConstant, std::size_t N=IntegralConstant::type::value>
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constexpr make_limit_f<N> operator()(IntegralConstant) const
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{
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return {};
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}
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};
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}
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template<std::size_t N, class F>
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constexpr detail::limit_adaptor<N, F> limit_c(F f)
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{
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return detail::limit_adaptor<N, F>(static_cast<F&&>(f));
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}
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BOOST_HOF_DECLARE_STATIC_VAR(limit, detail::limit_f);
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}} // namespace boost::hof
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#endif
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