has_equality_operator.h

/*  This file is part of the Vc library. {{{
Copyright © 2014 Matthias Kretz <kretz@kde.org>

Redistribution and use in source and binary forms, with or without
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      documentation and/or other materials provided with the distribution.
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      names of its contributors may be used to endorse or promote products
      derived from this software without specific prior written permission.

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ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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}}}*/

#ifndef VC_TRAITS_HAS_EQUALITY_OPERATOR_H_
#define VC_TRAITS_HAS_EQUALITY_OPERATOR_H_

namespace has_equality_operator_impl
{

template <typename T, typename U,
          typename = enable_if<!std::is_same<void, decltype(std::declval<T>() == std::declval<U>())>::value>>
std::true_type test(int);
template <typename T, typename U> std::false_type test(...);

}  // namespace has_equality_operator_impl

template <typename T, typename U = T>
struct has_equality_operator : public decltype(has_equality_operator_impl::test<T, U>(1))
{
};

static_assert(has_equality_operator<int>::value, "has_equality_operator fails");
namespace
{
class Foobar {};
static_assert(!has_equality_operator<Foobar>::value, "has_equality_operator fails");
} // unnamed namespace

#endif  // VC_TRAITS_HAS_EQUALITY_OPERATOR_H_