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/*!
@file
Defines `boost::hana::to` and related utilities.
@copyright Louis Dionne 2013-2016
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_HANA_CORE_TO_HPP
#define BOOST_HANA_CORE_TO_HPP
#include <boost/hana/fwd/core/to.hpp>
#include <boost/hana/concept/constant.hpp>
#include <boost/hana/concept/foldable.hpp>
#include <boost/hana/concept/sequence.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/common.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/core/make.hpp>
#include <boost/hana/detail/wrong.hpp>
#include <boost/hana/unpack.hpp>
#include <boost/hana/value.hpp>
#include <type_traits>
#include <utility>
BOOST_HANA_NAMESPACE_BEGIN
//////////////////////////////////////////////////////////////////////////
// to
//////////////////////////////////////////////////////////////////////////
//! @cond
template <typename To, typename From, typename>
struct to_impl : to_impl<To, From, when<true>> { };
//! @endcond
namespace convert_detail {
struct no_conversion { };
template <typename ...>
struct is_valid { static constexpr bool value = true; };
}
template <typename To, typename From, bool condition>
struct to_impl<To, From, when<condition>> : convert_detail::no_conversion {
template <typename X>
static constexpr auto apply(X const&) {
static_assert(detail::wrong<to_impl<To, From>, X>{},
"no conversion is available between the provided types");
}
};
template <typename To, typename From>
struct to_impl<To, From, when<convert_detail::is_valid<
decltype(static_cast<To>(std::declval<From>()))
>::value>> {
template <typename X>
static constexpr To apply(X&& x)
{ return static_cast<To>(static_cast<X&&>(x)); }
};
template <typename To>
struct to_impl<To, To> : embedding<> {
template <typename X>
static constexpr X apply(X&& x)
{ return static_cast<X&&>(x); }
};
//! @cond
template <typename To>
template <typename X>
constexpr decltype(auto) to_t<To>::operator()(X&& x) const {
using From = typename hana::tag_of<X>::type;
return to_impl<To, From>::apply(static_cast<X&&>(x));
}
//! @endcond
#define BOOST_HANA_DEFINE_EMBEDDING_IMPL(TO, FROM) \
template <> \
struct to_impl<TO, FROM> : embedding<> \
{ static constexpr TO apply(FROM x) { return x; } } \
/**/
BOOST_HANA_DEFINE_EMBEDDING_IMPL(long double, double);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(long double, float);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(double , float);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(signed long long, signed long);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(signed long long, signed int);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(signed long long, signed short);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(signed long long, signed char);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(signed long , signed int);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(signed long , signed short);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(signed long , signed char);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(signed int , signed short);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(signed int , signed char);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(signed short , signed char);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(unsigned long long, unsigned long);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(unsigned long long, unsigned int);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(unsigned long long, unsigned short);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(unsigned long long, unsigned char);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(unsigned long , unsigned int);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(unsigned long , unsigned short);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(unsigned long , unsigned char);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(unsigned int , unsigned short);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(unsigned int , unsigned char);
BOOST_HANA_DEFINE_EMBEDDING_IMPL(unsigned short , unsigned char);
#undef BOOST_HANA_DEFINE_EMBEDDING_IMPL
namespace detail {
template <typename T>
struct copy_char_signedness {
using type = typename std::conditional<std::is_signed<char>::value,
std::make_signed<T>, std::make_unsigned<T>
>::type::type;
};
}
// If `char` is signed, we define an embedding from `char` to any signed
// integral type. Otherwise, we define one from `char` to any unsigned
// integral type.
#define BOOST_HANA_DEFINE_CHAR_EMBEDDING_IMPL(TO) \
template <> \
struct to_impl<detail::copy_char_signedness<TO>::type, char> \
: embedding<> \
{ \
static constexpr detail::copy_char_signedness<TO>::type \
apply(char x) \
{ return x; } \
} \
/**/
BOOST_HANA_DEFINE_CHAR_EMBEDDING_IMPL(long long);
BOOST_HANA_DEFINE_CHAR_EMBEDDING_IMPL(long);
BOOST_HANA_DEFINE_CHAR_EMBEDDING_IMPL(int);
BOOST_HANA_DEFINE_CHAR_EMBEDDING_IMPL(short);
#undef BOOST_HANA_DEFINE_CHAR_EMBEDDING_IMPL
template <typename T>
struct to_impl<T*, decltype(nullptr)> : embedding<> {
static constexpr T* apply(decltype(nullptr)) { return nullptr; }
};
//////////////////////////////////////////////////////////////////////////
// is_convertible
//////////////////////////////////////////////////////////////////////////
template <typename From, typename To, typename>
struct is_convertible : std::true_type { };
template <typename From, typename To>
struct is_convertible<From, To, decltype((void)
static_cast<convert_detail::no_conversion>(*(to_impl<To, From>*)0)
)> : std::false_type { };
//////////////////////////////////////////////////////////////////////////
// is_embedded
//////////////////////////////////////////////////////////////////////////
template <typename From, typename To, typename>
struct is_embedded : std::false_type { };
template <typename From, typename To>
struct is_embedded<From, To, decltype((void)
static_cast<embedding<true>>(*(to_impl<To, From>*)0)
)> : std::true_type { };
//////////////////////////////////////////////////////////////////////////
// Conversion for Constants
//////////////////////////////////////////////////////////////////////////
template <typename To, typename From>
struct to_impl<To, From, when<
hana::Constant<From>::value &&
is_convertible<typename From::value_type, To>::value
>> : embedding<is_embedded<typename From::value_type, To>::value> {
template <typename X>
static constexpr decltype(auto) apply(X const&)
{ return hana::to<To>(hana::value<X>()); }
};
//////////////////////////////////////////////////////////////////////////
// Foldable -> Sequence
//////////////////////////////////////////////////////////////////////////
template <typename S, typename F>
struct to_impl<S, F, when<
hana::Sequence<S>::value &&
hana::Foldable<F>::value
>> : embedding<Sequence<F>::value> {
template <typename Xs>
static constexpr decltype(auto) apply(Xs&& xs)
{ return hana::unpack(static_cast<Xs&&>(xs), hana::make<S>); }
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_CORE_TO_HPP
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