NullablePointer.h

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#pragma once

#include <scl/macros.h>
#include <scl/tools/meta/constexpr_assert.h>
#include <scl/tools/meta/exists.h>
#include <scl/tools/meta/is_convertible.h>
#include <scl/concepts/AssignableWith.h>
#include <scl/concepts/Constructible.h>
#include <scl/concepts/DefaultConstructible.h>
#include <scl/concepts/InequalityComparable.h>
#include <scl/concepts/EqualityComparableWith.h>
#include <scl/concepts/InequalityComparableWith.h>

namespace scl{
    namespace concepts{
        template <class T>
        struct NullablePointer{
            constexpr operator bool() const{
                static_assert(AssignableWith<T, std::nullptr_t>{}, "");

                static_assert(META::is_convertible<decltype(
                    std::declval<T>() = nullptr
                ), T&>(), "NullablePointer<T>: Assignment should return a reference");

                return META::constexpr_assert<
                    Constructible<T, std::nullptr_t>{}
                    && DefaultConstructible<T>{}
                    && InequalityComparable<T>{}
                    && EqualityComparableWith<T, std::nullptr_t>{}
                    && EqualityComparableWith<std::nullptr_t, T>{}
                    && InequalityComparableWith<T, std::nullptr_t>{}
                    && InequalityComparableWith<std::nullptr_t, T>{}
                >();
            }
        };
    }
}