Dump into output stream (procedural vs functional style)

In today post will be short. In one of my unit test I wanted to dump acquired MQTT messages as map of topic, payload pairs (map<string, string>) into console output for debug purpose. This can be done an easy way in C++17 with following code

for (auto const & [topic, payload] : data)
	cout << topic << " -> " << payload << ", ";

The last couple of months, I’ve had a change to try JS (with Ramda functional library) so I wanted to know how eqvivalent functional code would look like in C++20’s ranges or using Boost.Ranges.

So functional style with C++20’s std::ranges

// functional with std::ranges
copy(data|
	transform([](auto const & e){
		return e.first + " -> "s + e.second;
	}),
	std::ostream_iterator<string>{cout, ", "}
);  //= a -> 1, b -> 2, c -> 3,

and the same, but in Boost.Ranges

// functional with Boost.Ranges
boost::copy(data|
	boost::adaptors::transformed([](auto const & e){
		return e.first + " -> "s + e.second;
	}),
	std::ostream_iterator<string>{cout, ", "}
);  //= a -> 1, b -> 2, c -> 3,

where data looks this way

map<string, string> data{  // (topic, payload) pair
	{"a", "1"},
	{"b", "2"},
	{"c", "3"}
};

there is the full code sample.

Just for a sake of debugging unit test it is easier to use procedural approach (the first one) and get work done over the functional one.