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Add SFINAE-friendly version of std::common_type (#298)

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It should help to improve uses of SFINAE like the one from #295
and fix #289 for MSVC 14.0 (VS2015) for good.

Copied from Boost.Hana.
This commit is contained in:
Mateusz Łoskot
2019-05-02 14:38:21 +02:00
committed by GitHub
parent 6832ad6ac6
commit d36a2c8edf
2 changed files with 57 additions and 12 deletions
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39
include/boost/gil/detail/std_common_type.hpp Normal file
View File

@@ -0,0 +1,39 @@
//
// Copyright Louis Dionne 2013-2017
//
// 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_GIL_DETAIL_STD_COMMON_TYPE_HPP
#define BOOST_GIL_DETAIL_STD_COMMON_TYPE_HPP
#include <type_traits>
#include <utility>
namespace boost { namespace gil { namespace detail {
// Defines a SFINAE-friendly version of `std::common_type`.
//
// Based on boost/hana/detail/std_common_type.hpp
// Equivalent to `std::common_type`, except it is SFINAE-friendly and
// does not support custom specializations.
template <typename T, typename U, typename = void>
struct std_common_type {};
template <typename T, typename U>
struct std_common_type
<
T, U,
decltype((void)(true ? std::declval<T>() : std::declval<U>()))
>
{
using type = typename std::decay
<
decltype(true ? std::declval<T>() : std::declval<U>())
>::type;
};
}}} // namespace boost::gil::detail
#endif

30
include/boost/gil/point.hpp
View File

@@ -9,6 +9,7 @@
#define BOOST_GIL_POINT_HPP
#include <boost/gil/utilities.hpp>
#include <boost/gil/detail/std_common_type.hpp>
#include <boost/config.hpp>
@@ -165,10 +166,15 @@ point<T> operator-(const point<T>& p1, const point<T>& p2)
/// \ingroup PointModel
template <typename T, typename D>
BOOST_FORCEINLINE
auto operator/(point<T> const& p, D d) -> point<typename std::common_type<T, D>::type>
auto operator/(point<T> const& p, D d)
-> typename std::enable_if
<
std::is_arithmetic<D>::value,
point<typename detail::std_common_type<T, D>::type>
>::type
{
static_assert(std::is_arithmetic<D>::value, "denominator is not arithmetic type");
using result_type = typename std::common_type<T, D>::type;
using result_type = typename detail::std_common_type<T, D>::type;
if (d < 0 || 0 < d)
{
double const x = p.x / static_cast<double>(d);
@@ -188,13 +194,13 @@ template <typename T, typename M>
BOOST_FORCEINLINE
auto operator*(point<T> const& p, M m)
-> typename std::enable_if
<
std::is_arithmetic<M>::value,
point<typename std::common_type<T, M>::type>
>::type
<
std::is_arithmetic<M>::value,
point<typename detail::std_common_type<T, M>::type>
>::type
{
static_assert(std::is_arithmetic<M>::value, "multiplier is not arithmetic type");
using result_type = typename std::common_type<T, M>::type;
using result_type = typename detail::std_common_type<T, M>::type;
return point<result_type>{p.x * m, p.y * m};
}
@@ -203,13 +209,13 @@ template <typename T, typename M>
BOOST_FORCEINLINE
auto operator*(M m, point<T> const& p)
-> typename std::enable_if
<
std::is_arithmetic<M>::value,
point<typename std::common_type<T, M>::type>
>::type
<
std::is_arithmetic<M>::value,
point<typename detail::std_common_type<T, M>::type>
>::type
{
static_assert(std::is_arithmetic<M>::value, "multiplier is not arithmetic type");
using result_type = typename std::common_type<T, M>::type;
using result_type = typename detail::std_common_type<T, M>::type;
return point<result_type>{p.x * m, p.y * m};
}