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#include <iostream>
#include <string>
#include <typeinfo>
using namespace std;
 
template<class T>
class Type_Identifier;
 
template<class T>
struct A
{
	const A& get_refrence(){
		return *this;
	}
};
 
 
template<class T>
void test(T&& t){//T&& bayad bashe na T&
	auto& var = t.get_refrence();
 
	Type_Identifier < decltype(var)> a;
}
 
int main()
{
	test(A<float>());
	test(A<std::string>());
}

prog.cpp: In instantiation of ‘void test(T&&) [with T = A<float>]’:
prog.cpp:27:17:   required from here
prog.cpp:22:35: error: ‘Type_Identifier<const A<float>&> a’ has incomplete type
  Type_Identifier < decltype(var)> a;
                                   ^
prog.cpp: In instantiation of ‘void test(T&&) [with T = A<std::basic_string<char> >]’:
prog.cpp:28:23:   required from here
prog.cpp:22:35: error: ‘Type_Identifier<const A<std::basic_string<char> >&> a’ has incomplete type

Standard output is empty