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#include <iostream>
#include <string>
 
template <class In, class Out>
struct Pipe
{
	typedef In in_type ;
	typedef Out out_type ;
 
	In in_val ;
 
	Pipe (const in_type &in_val = in_type()) : in_val (in_val)
	{
	}
 
	virtual auto operator () () const -> out_type
	{
		return out_type () ;
	}
};
 
template <class In, class Out, class Out2>
auto operator>> (const Pipe <In, Out> &lhs, Pipe <Out, Out2> &rhs) -> Pipe <Out, Out2>&
{
	rhs = lhs () ;
	return rhs ;
}
 
template <class In, class Out>
auto operator>> (const Pipe <In, Out> &lhs, Out &rhs) -> Out&
{
	rhs = lhs () ;
	return rhs ;
}
 
struct StringToInt : public Pipe <std::string, int>
{
	StringToInt (const std::string &s = "") : Pipe <in_type, out_type> (s)
	{
	}
 
	auto operator () () const -> out_type
	{
		return std::stoi (in_val) ;
	}
};
 
struct IntSquare : public Pipe <int, int>
{
	IntSquare (int n = 0) : Pipe <in_type, out_type> (n)
	{
	}
 
	auto operator () () const -> out_type
	{
		return in_val * in_val ;
	}
};
 
struct DivideBy42F : public Pipe <int, float>
{
	DivideBy42F (int n = 0) : Pipe <in_type, out_type> (n)
	{
	}
 
	auto operator () () const -> out_type
	{
		return static_cast <float> (in_val) / 42.0f ;
	}
};
 
int main ()
{
	float out = 0 ;
	StringToInt ("42") >> IntSquare () >> DivideBy42F () >> out ;
	std::cout << out << "\n" ;
 
	return 0 ;
}
 

prog.cpp: In function ‘int main()’:
prog.cpp:75:21: error: no match for ‘operator>>’ (operand types are ‘StringToInt’ and ‘IntSquare’)
  StringToInt ("42") >> IntSquare () >> DivideBy42F () >> out ;
                     ^
prog.cpp:75:21: note: candidates are:
prog.cpp:23:6: note: Pipe<Out, Out2>& operator>>(const Pipe<In, Out>&, Pipe<Out, Out2>&) [with In = std::basic_string<char>; Out = int; Out2 = int]
 auto operator>> (const Pipe <In, Out> &lhs, Pipe <Out, Out2> &rhs) -> Pipe <Out, Out2>&
      ^
prog.cpp:23:6: note:   no known conversion for argument 2 from ‘IntSquare’ to ‘Pipe<int, int>&’
prog.cpp:30:6: note: template<class In, class Out> Out& operator>>(const Pipe<In, Out>&, Out&)
 auto operator>> (const Pipe <In, Out> &lhs, Out &rhs) -> Out&
      ^
prog.cpp:30:6: note:   template argument deduction/substitution failed:
prog.cpp:75:35: note:   deduced conflicting types for parameter ‘Out’ (‘int’ and ‘IntSquare’)
  StringToInt ("42") >> IntSquare () >> DivideBy42F () >> out ;
                                   ^

Standard output is empty