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#include <iostream>
#include <string>
using namespace std;
 
class function_set {
public:
	static void override() { cout << "1" << endl; }
	static void override( const char* ) { cout << "2" << endl; }
	static void override( string ) { cout << "2" << endl; }
};
 
#define probe1( funct, ... ) funct( __VA_ARGS__ )
 
template < class f, class ... ax > auto probe2( f && funct, ax ... args ) -> decltype( funct( args ... ) ) {
	return funct( args ... );
}
 
int main() {
	probe1( function_set::override, "abc" );
	probe2( function_set::override, "abc" );
}

prog.cpp: In function ‘int main()’:
prog.cpp:20:40: error: no matching function for call to ‘probe2(<unresolved overloaded function type>, const char [4])’
  probe2( function_set::override, "abc" );
                                        ^
prog.cpp:20:40: note: candidate is:
prog.cpp:14:41: note: template<class f, class ... ax> decltype (funct(probe2::args ...)) probe2(f&&, ax ...)
 template < class f, class ... ax > auto probe2( f && funct, ax ... args ) -> decltype( funct( args ... ) ) {
                                         ^
prog.cpp:14:41: note:   template argument deduction/substitution failed:
prog.cpp:20:40: note:   couldn't deduce template parameter ‘f’
  probe2( function_set::override, "abc" );
                                        ^

Standard output is empty