test/cpp/test_copy_elision.cpp

#include <iostream>
#include <exception>
#include <string>
#include <algorithm>

struct copy_tracker
{
	int v;

	copy_tracker()
		: v(0)
	{
		std::cout << "copy_tracker::copy_tracker()" << std::endl;
	}

	copy_tracker( const copy_tracker& c )
		: v( c.v )
	{
		std::cout << "copy_tracker::copy_tracker( const copy_tracker& c )" << std::endl;
	}

	copy_tracker( copy_tracker&& c )
		: v( c.v )
	{
		std::cout << "copy_tracker::copy_tracker( copy_tracker&& c )  MOVE " << std::endl;
	}

	void use_object()
	{
		std::cout << v << std::endl;
	}
};

template <int n>
copy_tracker return_by_value()
{
	return return_by_value<n-1>();
}
template <>
copy_tracker return_by_value<1>()
{
	return copy_tracker();
}

template <int n>
copy_tracker return_by_value2()
{
	copy_tracker o = return_by_value2<n-1>();
	o.v = n;
	return o;
}
template <>
copy_tracker return_by_value2<1>()
{
	copy_tracker o; //return value optimization still applies.
	o.v = 1;
	return o;
}

template <int n>
copy_tracker static_by_value()
{
	return static_by_value<n-1>();
}
template <>
copy_tracker static_by_value<1>()
{
	static copy_tracker o; //return value optimization still applies.
	return o;
}


template <int n>
copy_tracker move_by_value()
{
	return std::move(move_by_value<n-1>());
}
template <>
copy_tracker move_by_value<1>()
{
	return copy_tracker(); //return value optimization still applies.
}


template <int n>
void pass_by_value(copy_tracker o)
{
	pass_by_value<n-1>(std::move(o));
//	o.v = n;
//	o.use_object();
}
template <>
void pass_by_value<1>(copy_tracker o)
{
	o.use_object();
}


void test_copy_tracker()
{
	std::cout << "---------------------------------------------------------" 
				<< std::endl << std::endl;
	
	std::cout << "Return by value and assign." << std::endl;
	{ copy_tracker o = return_by_value<10>(); }
	std::cout << "---------------------------------------------------------" 
				<< std::endl << std::endl;

	std::cout << "Return by named value and assign." << std::endl;
	{ copy_tracker o = return_by_value2<10>(); }
	std::cout << "---------------------------------------------------------" 
				<< std::endl << std::endl;

	std::cout << "Return static and assign." << std::endl;
	{ copy_tracker o = static_by_value<10>(); }
	std::cout << "---------------------------------------------------------" 
				<< std::endl << std::endl;
	
	std::cout << "Move value and assign." << std::endl;
	{ copy_tracker o = move_by_value<10>(); }
	std::cout << "---------------------------------------------------------" 
				<< std::endl << std::endl;

	std::cout << "Pass lvalue." << std::endl;
	{ copy_tracker o = return_by_value<10>();
	  pass_by_value<1>( o ); }
	std::cout << "---------------------------------------------------------" 
				<< std::endl << std::endl;

	std::cout << "Pass by intermediately captured rvalue." << std::endl;
	{ const copy_tracker& o = return_by_value<10>();
	  pass_by_value<1>( o ); }
	std::cout << "---------------------------------------------------------" 
				<< std::endl << std::endl;
	
	std::cout << "Pass by intermediately captured rvalue." << std::endl;
	{ const copy_tracker& o = return_by_value<10>();
	  pass_by_value<1>( static_cast<copy_tracker&&>(const_cast<copy_tracker&>(o)) ); }
	std::cout << "---------------------------------------------------------" 
				<< std::endl << std::endl;

	std::cout << "Pass rvalue directly." << std::endl;
	{ pass_by_value<1>( return_by_value<10>() ); }
	std::cout << "---------------------------------------------------------" 
				<< std::endl << std::endl;
	
	std::cout << "Pass rvalue directly." << std::endl;
	{ pass_by_value<2>( return_by_value<10>() ); }
	std::cout << "---------------------------------------------------------" 
				<< std::endl << std::endl;
}

int main ( void )
{try{

	test_copy_tracker();
	return 0;
}
catch ( const std::exception& e )
{
	std::cerr << std::endl
			<< "std::exception(\"" << e.what() << "\")." << std::endl;
}
catch ( ... )
{
	std::cerr  << std::endl
			<< "unknown exception." << std::endl;
}}