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#include <iostream>
#include <map>
using namespace std;
 
template <typename T1, typename T2>
void swap_pair(std::pair<T1, T2>& pair)
{
	T2 tmp(std::move(pair.first));
	pair.first = std::move(pair.second);
	pair.second = std::move(tmp);
}
 
template <typename K, typename V>
void swap_map(std::map<K, V>& map)
{
	for (auto& kv_pair : map)
		swap_pair(kv_pair);
}
 
int main() {
	std::map<int, int> foo;
	swap_map(foo);
	return 0;
}

prog.cpp: In instantiation of ‘void swap_pair(std::pair<_T1, _T2>&) [with T1 = const int; T2 = int]’:
prog.cpp:17:20:   required from ‘void swap_map(std::map<K, V>&) [with K = int; V = int]’
prog.cpp:22:14:   required from here
prog.cpp:9:13: error: assignment of read-only member ‘std::pair<const int, int>::first’
  pair.first = std::move(pair.second);
             ^

Standard output is empty