106 lines
3.3 KiB
C++
106 lines
3.3 KiB
C++
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/*!
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@file
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Defines `boost::hana::partial`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_FUNCTIONAL_PARTIAL_HPP
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#define BOOST_HANA_FUNCTIONAL_PARTIAL_HPP
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#include <boost/hana/basic_tuple.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/detail/decay.hpp>
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#include <cstddef>
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#include <utility>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @ingroup group-functional
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//! Partially apply a function to some arguments.
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//!
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//! Given a function `f` and some arguments, `partial` returns a new
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//! function corresponding to the partially applied function `f`. This
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//! allows providing some arguments to a function and letting the rest
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//! of the arguments be provided later. Specifically, `partial(f, x...)`
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//! is a function such that
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//! @code
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//! partial(f, x...)(y...) == f(x..., y...)
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//! @endcode
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//!
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//! @note
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//! The arity of `f` must match the total number of arguments passed to
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//! it, i.e. `sizeof...(x) + sizeof...(y)`.
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//!
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//!
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//! Example
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//! -------
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//! @include example/functional/partial.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto partial = [](auto&& f, auto&& ...x) {
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return [perfect-capture](auto&& ...y) -> decltype(auto) {
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return forwarded(f)(forwarded(x)..., forwarded(y)...);
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};
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};
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#else
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template <typename Indices, typename F, typename ...X>
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struct partial_t;
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struct make_partial_t {
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struct secret { };
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template <typename F, typename ...X>
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constexpr partial_t<
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std::make_index_sequence<sizeof...(X)>,
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typename detail::decay<F>::type,
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typename detail::decay<X>::type...
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>
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operator()(F&& f, X&& ...x) const {
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return {secret{}, static_cast<F&&>(f), static_cast<X&&>(x)...};
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}
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};
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template <std::size_t ...n, typename F, typename ...X>
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struct partial_t<std::index_sequence<n...>, F, X...> {
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partial_t() = default;
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template <typename ...T>
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constexpr partial_t(make_partial_t::secret, T&& ...t)
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: storage_{static_cast<T&&>(t)...}
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{ }
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basic_tuple<F, X...> storage_;
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template <typename ...Y>
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constexpr decltype(auto) operator()(Y&& ...y) const& {
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return hana::get_impl<0>(storage_)(
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hana::get_impl<n+1>(storage_)...,
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static_cast<Y&&>(y)...
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);
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}
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template <typename ...Y>
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constexpr decltype(auto) operator()(Y&& ...y) & {
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return hana::get_impl<0>(storage_)(
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hana::get_impl<n+1>(storage_)...,
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static_cast<Y&&>(y)...
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);
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}
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template <typename ...Y>
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constexpr decltype(auto) operator()(Y&& ...y) && {
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return static_cast<F&&>(hana::get_impl<0>(storage_))(
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static_cast<X&&>(hana::get_impl<n+1>(storage_))...,
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static_cast<Y&&>(y)...
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);
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}
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};
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constexpr make_partial_t partial{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FUNCTIONAL_PARTIAL_HPP
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