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[core] Add embedding from char to any integral type with proper signedness

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This commit is contained in:
Louis Dionne
2016-02-11 10:59:26 -05:00
parent 31aa2e6f60
commit 7f7c7a19a9
2 changed files with 53 additions and 1 deletions
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30
include/boost/hana/core/to.hpp
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@@ -107,12 +107,40 @@ BOOST_HANA_NAMESPACE_BEGIN
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; }
};
#undef BOOST_HANA_DEFINE_EMBEDDING_IMPL
//////////////////////////////////////////////////////////////////////////
// is_convertible

24
test/core/is_embedded.cpp
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@@ -3,6 +3,9 @@
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
#include <boost/hana/core/to.hpp>
#include <boost/hana/equal.hpp>
#include <climits>
namespace hana = boost::hana;
@@ -35,4 +38,25 @@ static_assert(hana::is_embedded<unsigned short, unsigned int>{}, "");
static_assert(hana::is_embedded<unsigned char, unsigned int>{}, "");
static_assert(hana::is_embedded<unsigned char, unsigned short>{}, "");
#if CHAR_MIN < 0 // char is signed
static_assert(hana::is_embedded<char, signed long long>{}, "");
static_assert(hana::is_embedded<char, signed long>{}, "");
static_assert(hana::is_embedded<char, signed int>{}, "");
static_assert(hana::is_embedded<char, signed short>{}, "");
static_assert(hana::equal('a', static_cast<signed int>('a')), "");
#else // char is unsigned
static_assert(hana::is_embedded<char, unsigned long long>{}, "");
static_assert(hana::is_embedded<char, unsigned long>{}, "");
static_assert(hana::is_embedded<char, unsigned int>{}, "");
static_assert(hana::is_embedded<char, unsigned short>{}, "");
static_assert(hana::equal('a', static_cast<unsigned int>('a')), "");
#endif
int main() { }