template_helpers.hpp

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// SPDX-License-Identifier: BSD-3-Clause
/* Copyright 2019-2020, Intel Corporation */
 
#ifndef LIBPMEMOBJ_CPP_TEMPLATE_HELPERS_HPP
#define LIBPMEMOBJ_CPP_TEMPLATE_HELPERS_HPP
 
#include <type_traits>
 
namespace pmem
{
 
namespace detail
{
 
template <typename... Ts>
struct make_void {
    typedef void type;
};
template <typename... Ts>
using void_t = typename make_void<Ts...>::type;
 
/* Generic SFINAE helper for expression checks, based on the idea demonstrated
 * in ISO C++ paper n4502 */
template <typename T, typename, template <typename> class... Checks>
struct supports_impl {
    using type = std::false_type;
};
template <typename T, template <typename> class... Checks>
struct supports_impl<T, void_t<Checks<T>...>, Checks...> {
    using type = std::true_type;
};
 
template <typename T, template <typename> class... Checks>
using supports = typename supports_impl<T, void, Checks...>::type;
 
template <typename Compare>
using is_transparent = typename Compare::is_transparent;
 
template <typename Compare>
using has_is_transparent = detail::supports<Compare, is_transparent>;
 
} /* namespace detail */
 
} /* namespace pmem */
 
#endif /* LIBPMEMOBJ_CPP_TEMPLATE_HELPERS_HPP */