418 lines
16 KiB
C++
418 lines
16 KiB
C++
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/*!
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@file
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Defines `boost::hana::optional`.
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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_OPTIONAL_HPP
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#define BOOST_HANA_OPTIONAL_HPP
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#include <boost/hana/fwd/optional.hpp>
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#include <boost/hana/bool.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/tag_of.hpp>
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#include <boost/hana/detail/decay.hpp>
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#include <boost/hana/detail/operators/adl.hpp>
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#include <boost/hana/detail/operators/comparable.hpp>
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#include <boost/hana/detail/operators/monad.hpp>
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#include <boost/hana/detail/operators/orderable.hpp>
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#include <boost/hana/detail/wrong.hpp>
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#include <boost/hana/functional/partial.hpp>
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#include <boost/hana/fwd/any_of.hpp>
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#include <boost/hana/fwd/ap.hpp>
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#include <boost/hana/fwd/concat.hpp>
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#include <boost/hana/fwd/core/make.hpp>
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#include <boost/hana/fwd/empty.hpp>
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#include <boost/hana/fwd/equal.hpp>
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#include <boost/hana/fwd/find_if.hpp>
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#include <boost/hana/fwd/flatten.hpp>
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#include <boost/hana/fwd/less.hpp>
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#include <boost/hana/fwd/lift.hpp>
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#include <boost/hana/fwd/transform.hpp>
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#include <boost/hana/fwd/type.hpp>
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#include <boost/hana/fwd/unpack.hpp>
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#include <cstddef> // std::nullptr_t
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#include <type_traits>
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#include <utility>
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BOOST_HANA_NAMESPACE_BEGIN
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//////////////////////////////////////////////////////////////////////////
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// optional<>
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//////////////////////////////////////////////////////////////////////////
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namespace detail {
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template <typename T, typename = typename hana::tag_of<T>::type>
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struct nested_type { };
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template <typename T>
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struct nested_type<T, type_tag> { using type = typename T::type; };
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}
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template <typename T>
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struct optional<T> : detail::operators::adl<>, detail::nested_type<T> {
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// 5.3.1, Constructors
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constexpr optional() = default;
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constexpr optional(optional const&) = default;
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constexpr optional(optional&&) = default;
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constexpr optional(T const& t)
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: value_(t)
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{ }
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constexpr optional(T&& t)
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: value_(static_cast<T&&>(t))
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{ }
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// 5.3.3, Assignment
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constexpr optional& operator=(optional const&) = default;
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constexpr optional& operator=(optional&&) = default;
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// 5.3.5, Observers
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constexpr T const* operator->() const { return &value_; }
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constexpr T* operator->() { return &value_; }
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constexpr T& value() & { return value_; }
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constexpr T const& value() const& { return value_; }
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constexpr T&& value() && { return static_cast<T&&>(value_); }
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constexpr T const&& value() const&& { return static_cast<T const&&>(value_); }
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constexpr T& operator*() & { return value_; }
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constexpr T const& operator*() const& { return value_; }
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constexpr T&& operator*() && { return static_cast<T&&>(value_); }
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constexpr T const&& operator*() const&& { return static_cast<T const&&>(value_); }
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template <typename U> constexpr T& value_or(U&&) & { return value_; }
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template <typename U> constexpr T const& value_or(U&&) const& { return value_; }
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template <typename U> constexpr T&& value_or(U&&) && { return static_cast<T&&>(value_); }
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template <typename U> constexpr T const&& value_or(U&&) const&& { return static_cast<T const&&>(value_); }
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// We leave this public because it simplifies the implementation, but
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// this should be considered private by users.
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T value_;
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};
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//! @cond
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template <typename ...dummy>
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constexpr auto optional<>::value() const {
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static_assert(detail::wrong<dummy...>{},
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"hana::optional::value() requires a non-empty optional");
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}
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template <typename ...dummy>
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constexpr auto optional<>::operator*() const {
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static_assert(detail::wrong<dummy...>{},
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"hana::optional::operator* requires a non-empty optional");
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}
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template <typename U>
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constexpr U&& optional<>::value_or(U&& u) const {
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return static_cast<U&&>(u);
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}
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template <typename T>
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constexpr auto make_just_t::operator()(T&& t) const {
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return hana::optional<typename detail::decay<T>::type>(static_cast<T&&>(t));
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}
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//! @endcond
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template <typename ...T>
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struct tag_of<optional<T...>> {
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using type = optional_tag;
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};
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//////////////////////////////////////////////////////////////////////////
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// make<optional_tag>
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct make_impl<optional_tag> {
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template <typename X>
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static constexpr auto apply(X&& x)
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{ return hana::just(static_cast<X&&>(x)); }
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static constexpr auto apply()
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{ return hana::nothing; }
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};
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//////////////////////////////////////////////////////////////////////////
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// Operators
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//////////////////////////////////////////////////////////////////////////
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namespace detail {
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template <>
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struct comparable_operators<optional_tag> {
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static constexpr bool value = true;
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};
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template <>
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struct orderable_operators<optional_tag> {
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static constexpr bool value = true;
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};
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template <>
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struct monad_operators<optional_tag> {
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static constexpr bool value = true;
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};
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}
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//////////////////////////////////////////////////////////////////////////
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// is_just and is_nothing
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//////////////////////////////////////////////////////////////////////////
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//! @cond
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template <typename ...T>
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constexpr auto is_just_t::operator()(optional<T...> const&) const
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{ return hana::bool_c<sizeof...(T) != 0>; }
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template <typename ...T>
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constexpr auto is_nothing_t::operator()(optional<T...> const&) const
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{ return hana::bool_c<sizeof...(T) == 0>; }
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//! @endcond
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//////////////////////////////////////////////////////////////////////////
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// sfinae
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//////////////////////////////////////////////////////////////////////////
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namespace detail {
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struct sfinae_impl {
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template <typename F, typename ...X, typename = decltype(
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std::declval<F>()(std::declval<X>()...)
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)>
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constexpr decltype(auto) operator()(int, F&& f, X&& ...x) const {
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using Return = decltype(static_cast<F&&>(f)(static_cast<X&&>(x)...));
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static_assert(!std::is_same<Return, void>::value,
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"hana::sfinae(f)(args...) requires f(args...) to be non-void");
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return hana::just(static_cast<F&&>(f)(static_cast<X&&>(x)...));
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}
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template <typename F, typename ...X>
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constexpr auto operator()(long, F&&, X&& ...) const
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{ return hana::nothing; }
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};
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}
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//! @cond
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template <typename F>
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constexpr decltype(auto) sfinae_t::operator()(F&& f) const {
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return hana::partial(detail::sfinae_impl{}, int{},
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static_cast<F&&>(f));
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}
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//! @endcond
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//////////////////////////////////////////////////////////////////////////
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// Comparable
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct equal_impl<optional_tag, optional_tag> {
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template <typename T, typename U>
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static constexpr auto apply(hana::optional<T> const& t, hana::optional<U> const& u)
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{ return hana::equal(t.value_, u.value_); }
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static constexpr hana::true_ apply(hana::optional<> const&, hana::optional<> const&)
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{ return {}; }
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template <typename T, typename U>
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static constexpr hana::false_ apply(T const&, U const&)
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{ return {}; }
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};
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//////////////////////////////////////////////////////////////////////////
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// Orderable
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct less_impl<optional_tag, optional_tag> {
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template <typename T>
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static constexpr hana::true_ apply(hana::optional<> const&, hana::optional<T> const&)
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{ return {}; }
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static constexpr hana::false_ apply(hana::optional<> const&, hana::optional<> const&)
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{ return {}; }
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template <typename T>
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static constexpr hana::false_ apply(hana::optional<T> const&, hana::optional<> const&)
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{ return {}; }
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template <typename T, typename U>
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static constexpr auto apply(hana::optional<T> const& x, hana::optional<U> const& y)
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{ return hana::less(x.value_, y.value_); }
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};
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//////////////////////////////////////////////////////////////////////////
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// Functor
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct transform_impl<optional_tag> {
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template <typename F>
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static constexpr auto apply(optional<> const&, F&&)
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{ return hana::nothing; }
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template <typename T, typename F>
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static constexpr auto apply(optional<T> const& opt, F&& f)
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{ return hana::just(static_cast<F&&>(f)(opt.value_)); }
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template <typename T, typename F>
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static constexpr auto apply(optional<T>& opt, F&& f)
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{ return hana::just(static_cast<F&&>(f)(opt.value_)); }
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template <typename T, typename F>
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static constexpr auto apply(optional<T>&& opt, F&& f)
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{ return hana::just(static_cast<F&&>(f)(static_cast<T&&>(opt.value_))); }
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};
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//////////////////////////////////////////////////////////////////////////
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// Applicative
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct lift_impl<optional_tag> {
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template <typename X>
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static constexpr auto apply(X&& x)
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{ return hana::just(static_cast<X&&>(x)); }
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};
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template <>
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struct ap_impl<optional_tag> {
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template <typename F, typename X>
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static constexpr auto ap_helper(F&&, X&&, ...)
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{ return hana::nothing; }
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template <typename F, typename X>
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static constexpr auto ap_helper(F&& f, X&& x, hana::true_, hana::true_)
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{ return hana::just(static_cast<F&&>(f).value_(static_cast<X&&>(x).value_)); }
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template <typename F, typename X>
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static constexpr auto apply(F&& f, X&& x) {
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return ap_impl::ap_helper(static_cast<F&&>(f), static_cast<X&&>(x),
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hana::is_just(f), hana::is_just(x));
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}
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};
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//////////////////////////////////////////////////////////////////////////
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// Monad
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct flatten_impl<optional_tag> {
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static constexpr auto apply(optional<> const&)
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{ return hana::nothing; }
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static constexpr auto apply(optional<optional<>> const&)
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{ return hana::nothing; }
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template <typename T>
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static constexpr auto apply(optional<optional<T>> const& opt)
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{ return hana::just(opt.value_.value_); }
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template <typename T>
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static constexpr auto apply(optional<optional<T>>&& opt)
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{ return hana::just(static_cast<T&&>(opt.value_.value_)); }
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};
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//////////////////////////////////////////////////////////////////////////
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// MonadPlus
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct concat_impl<optional_tag> {
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template <typename Y>
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static constexpr auto apply(hana::optional<>&, Y&& y)
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{ return static_cast<Y&&>(y); }
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template <typename Y>
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static constexpr auto apply(hana::optional<>&&, Y&& y)
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{ return static_cast<Y&&>(y); }
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template <typename Y>
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static constexpr auto apply(hana::optional<> const&, Y&& y)
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{ return static_cast<Y&&>(y); }
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template <typename X, typename Y>
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static constexpr auto apply(X&& x, Y&&)
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{ return static_cast<X&&>(x); }
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};
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template <>
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struct empty_impl<optional_tag> {
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static constexpr auto apply()
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{ return hana::nothing; }
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};
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//////////////////////////////////////////////////////////////////////////
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// Foldable
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct unpack_impl<optional_tag> {
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template <typename T, typename F>
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static constexpr decltype(auto) apply(optional<T>&& opt, F&& f)
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{ return static_cast<F&&>(f)(static_cast<T&&>(opt.value_)); }
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template <typename T, typename F>
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static constexpr decltype(auto) apply(optional<T> const& opt, F&& f)
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{ return static_cast<F&&>(f)(opt.value_); }
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template <typename T, typename F>
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static constexpr decltype(auto) apply(optional<T>& opt, F&& f)
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{ return static_cast<F&&>(f)(opt.value_); }
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template <typename F>
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static constexpr decltype(auto) apply(optional<> const&, F&& f)
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{ return static_cast<F&&>(f)(); }
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};
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//////////////////////////////////////////////////////////////////////////
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// Searchable
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//////////////////////////////////////////////////////////////////////////
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namespace detail {
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template <bool>
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struct optional_find_if {
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template <typename T>
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static constexpr auto apply(T const&)
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{ return hana::nothing; }
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};
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template <>
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struct optional_find_if<true> {
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template <typename T>
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static constexpr auto apply(T&& t)
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{ return hana::just(static_cast<T&&>(t)); }
|
||
|
|
};
|
||
|
|
}
|
||
|
|
|
||
|
|
template <>
|
||
|
|
struct find_if_impl<optional_tag> {
|
||
|
|
template <typename T, typename Pred>
|
||
|
|
static constexpr auto apply(hana::optional<T> const& opt, Pred&& pred) {
|
||
|
|
constexpr bool found = decltype(static_cast<Pred&&>(pred)(opt.value_))::value;
|
||
|
|
return detail::optional_find_if<found>::apply(opt.value_);
|
||
|
|
}
|
||
|
|
|
||
|
|
template <typename T, typename Pred>
|
||
|
|
static constexpr auto apply(hana::optional<T>& opt, Pred&& pred) {
|
||
|
|
constexpr bool found = decltype(static_cast<Pred&&>(pred)(opt.value_))::value;
|
||
|
|
return detail::optional_find_if<found>::apply(opt.value_);
|
||
|
|
}
|
||
|
|
|
||
|
|
template <typename T, typename Pred>
|
||
|
|
static constexpr auto apply(hana::optional<T>&& opt, Pred&& pred) {
|
||
|
|
constexpr bool found = decltype(
|
||
|
|
static_cast<Pred&&>(pred)(static_cast<T&&>(opt.value_))
|
||
|
|
)::value;
|
||
|
|
return detail::optional_find_if<found>::apply(static_cast<T&&>(opt.value_));
|
||
|
|
}
|
||
|
|
|
||
|
|
template <typename Pred>
|
||
|
|
static constexpr auto apply(hana::optional<> const&, Pred&&)
|
||
|
|
{ return hana::nothing; }
|
||
|
|
};
|
||
|
|
|
||
|
|
template <>
|
||
|
|
struct any_of_impl<optional_tag> {
|
||
|
|
template <typename T, typename Pred>
|
||
|
|
static constexpr auto apply(hana::optional<T> const& opt, Pred&& pred)
|
||
|
|
{ return static_cast<Pred&&>(pred)(opt.value_); }
|
||
|
|
|
||
|
|
template <typename Pred>
|
||
|
|
static constexpr hana::false_ apply(hana::optional<> const&, Pred&&)
|
||
|
|
{ return {}; }
|
||
|
|
};
|
||
|
|
BOOST_HANA_NAMESPACE_END
|
||
|
|
|
||
|
|
#endif // !BOOST_HANA_OPTIONAL_HPP
|