c++)배열을 정렬할 때 질문합니다..

#include <iostream>
#include <array>
#include <memory>
#include <random>
#include <algorithm>
 
using Row = std::array<int, 10>;
using Matrix = std::array<std::unique_ptr<Row>, 10>;
 
static int uniform_random_integer() {
	static constexpr int min = 0, max = 100;
 
	static std::random_device r;
	static std::default_random_engine engine{ r() };
	static std::uniform_int_distribution<int> uniform_dist(min, max);
 
	return uniform_dist(engine);
}
 
static std::ostream& operator<<(std::ostream& os, const Matrix& m) {
	std::ranges::for_each(m, [&os](const auto& r) { std::ranges::for_each(*r, [&os](const auto& elem) { os << elem << ' '; }); os << '\n'; });
 
	return os;
}
 
int main() {
	Matrix m;
 
	std::ranges::generate(m, []() { auto r = std::make_unique<Row>(); std::ranges::generate(*r, uniform_random_integer); return r; });
	std::cout << "initial matrix:\n" << m << '\n';
 
	std::ranges::for_each(m, [](const auto& r) { std::ranges::sort(*r); });
	std::cout << "after in-row sorting:\n" << m << '\n';
 
	std::ranges::sort(m, {}, [](const auto& r) { int sum = 0; std::ranges::for_each(*r, [&sum](const auto& elem) { sum += elem; }); return sum; });
	std::cout << "after row sorting:\n" << m << '\n';
 
	return 0;
}