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#include <iostream>
using namespace std;
 
struct POINT
{
	long x = 0;
	long y = 0;
};
 
template<typename RetType, typename ...Params>
struct func
{
	template<typename R, typename ...P>
	R operator()( P&&... p )
	{
	}
};
 
int main() 
{
	func<bool,long,long> f;
	POINT p { 1,2 };
	f( p.x, p.y );
	return 0;
}

prog.cpp: In function ‘int main()’:
prog.cpp:23:14: error: no match for call to ‘(func<bool, long int, long int>) (long int&, long int&)’
  f( p.x, p.y );
              ^
prog.cpp:14:4: note: candidate: template<class R, class ... P> R func<RetType, Params>::operator()(P&& ...) [with R = R; P = {P ...}; RetType = bool; Params = {long int, long int}]
  R operator()( P&&... p )
    ^~~~~~~~
prog.cpp:14:4: note:   template argument deduction/substitution failed:
prog.cpp:23:14: note:   couldn't deduce template parameter ‘R’
  f( p.x, p.y );
              ^

Standard output is empty