Инициализировать union константу в классе

static const TUnion A = TUnion(1,1);

$ g++ -std=c++14 -ggdb -o range range.cpp

test.cpp:74:36: error: ‘constexpr’ needed for in-class initialization of static data member ‘const TRangeLocation::TUnion TRangeLocation::A’ of non-integral type [-fpermissive]
  static const TUnion A = TUnion(1,1);
                                    ^
test.cpp:74:36: error: ‘constexpr TRangeLocation::TUnion::TUnion(TPointLocation::T, TPointLocation::T)’ called in a constant expression

#include <iostream>
#include <iomanip>
#include <cstdint> // uint8_t
#include <type_traits>

/**
 * \brief Definitions of constants for describing location of point relative of range's endpoints
 *
 * If was decided no not using enum since a bug in gcc: when defining bitsize of enum field, gcc emits warning: http://stackoverflow.com/questions/28401851/is-it-possible-to-specify-the-bit-width-of-an-enum-in-c11
 * All constants shall have same type
 * MAX shall contain maximum value
*/
class TPointLocation{ /// \todo: Rename to TPointRangeLocation
public:
	typedef uint8_t T; /// To let all constants have same type

	static const T LEFT_FROM = 0;  /// -p-f---t---
	static const T EQUAL_FROM = 1; /// ---fp--t---
	static const T BETWEEN = 2;    /// ---f-p-t---
	static const T EQUAL_TO = 3;   /// ---f---tp--
	static const T RIGHT_TO = 4;   /// ---f---t-p-

	static const T MAX = 4; /// Maximum value of all constants. Uses for static_assert.

	/// \todo: think about constexpr
};

/**
 * \brief Location of one range relative to another one.
*/
class TRangeLocation{ /// \todo: Rename to TRangeRangeLocation
public:
	typedef uint16_t T; /// Shall fit two TPointLocation::T

  /** \brief A structure just containing location information of two endpoints of the range.
	 *
	 * Used in union to construct cummulative value.
	 * Shall not be a bitfield, since later will use reference to it.
	 * Separated because a new struct cannot be defined in the union.
	*/
	struct TPoints{
		static_assert(std::is_integral<TPointLocation::T>::value && std::is_unsigned<TPointLocation::T>::value,"TPointLocation is expected to be an unsigned integer");
		//static_assert(TPointLocation::MAX < 9,"Bitfield size in not enough to store the value");
		static_assert(sizeof(T)==sizeof(TPointLocation::T)*2 ,"Size of TrangeLocation: is bigger (and thus causes ambiguity) or is not enough");
		TPointLocation::T from;
		TPointLocation::T to;

		constexpr TPoints():from(0),to(0){};
		constexpr TPoints(TPointLocation::T f, TPointLocation::T t):from(f),to(t){};
	};

	union TUnion{
		TPoints m_points; /// It is prefered to avoid constructions like m_points.from, but this is impossible
		T m_range;

		constexpr TUnion():m_range(0){};
		constexpr TUnion(TPointLocation::T from, TPointLocation::T to):m_points(from,to){};
	} m_value;

	const T &m_range = m_value.m_range; /// Convenient alias
	const TPointLocation::T &m_from = m_value.m_points.from; /// Convenient alias
	const TPointLocation::T &m_to = m_value.m_points.to;     /// Convenient alias

	TRangeLocation(){};
	TRangeLocation(TPointLocation::T from, TPointLocation::T to):m_value(from,to){};

	TRangeLocation& operator=(TRangeLocation &&b)
	{
		m_value.m_range = std::move(b.m_value.m_range);

		return *this;
	};

	static const TUnion A = TUnion(1,1);
} x;

int main()
{
	return 0;
};