The parameter or print function is a forwarding reference because the range can change while being iterated, but the current value is l-value reference:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | #include <string>#include <vector>#include <ranges>#include <iostream>template <class R, class Value>concept range_over = std::ranges::range<R> && std::same_as<std::ranges::range_value_t<R>, Value>;template <range_over<std::string> Range>void print(Range&& range){ for (const std::string& val : range) { std::cout << val << std::endl; }} |
18 19 20 21 22 23 24 25 26 27 | int main(){ std::vector<std::string> v = { "0abc", "1def", "2ghi", "1jkl" }; print(v); print(v | std::views::filter([](const std::string& val) { return val.starts_with('1'); })); return 0;} |
We call print with both a named variable and a temporary.
