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#include <string>
#include <type_traits>
 
template<typename T>
struct Point {
	using value_type = T;
	using self_type = Point<T>;
 
	value_type m_value;
 
    Point(value_type value) : m_value(value) {}
 
	template<typename RhsT,
		typename std::enable_if<
			std::is_arithmetic<value_type>::value
			&& std::is_arithmetic<RhsT>::value, int>::type = 0>
	self_type& operator = (const Point<RhsT>& rhs) {
		m_value = static_cast<value_type>(rhs.m_value);
		return *this;
	}
};
 
int main() {
	Point<int> a1(4);
	Point<int> a2(5);
	Point<double> a3(6.0);
	Point<std::string> a4("hello");
 
    a1 = a2;
    a2 = a3;
 
    a3 = a4;
 
	return 0;
}

prog.cpp: In function 'int main()':
prog.cpp:32:8: error: no match for 'operator=' (operand types are 'Point<double>' and 'Point<std::basic_string<char> >')
     a3 = a4;
        ^
prog.cpp:32:8: note: candidates are:
prog.cpp:17:13: note: template<class RhsT, typename std::enable_if<(std::is_arithmetic<double>::value && std::is_arithmetic<_Tp>::value), int>::type <anonymous> > Point<T>::self_type& Point<T>::operator=(const Point<RhsT>&) [with RhsT = RhsT; typename std::enable_if<(std::is_arithmetic<_Tp>::value && std::is_arithmetic<RhsT>::value), int>::type <anonymous> = <enumerator>; T = double]
  self_type& operator = (const Point<RhsT>& rhs) {
             ^
prog.cpp:17:13: note:   template argument deduction/substitution failed:
prog.cpp:16:53: error: no type named 'type' in 'struct std::enable_if<false, int>'
    && std::is_arithmetic<RhsT>::value, int>::type = 0>
                                                     ^
prog.cpp:16:53: note: invalid template non-type parameter
prog.cpp:5:8: note: Point<double>& Point<double>::operator=(const Point<double>&)
 struct Point {
        ^
prog.cpp:5:8: note:   no known conversion for argument 1 from 'Point<std::basic_string<char> >' to 'const Point<double>&'
prog.cpp:5:8: note: Point<double>& Point<double>::operator=(Point<double>&&)
prog.cpp:5:8: note:   no known conversion for argument 1 from 'Point<std::basic_string<char> >' to 'Point<double>&&'

Standard output is empty