I'm trying to build a view that takes a vector of strings, splits those strings into pieces on char ; and returns permutations for the resulting tokens on each line.
int main()
{
std::vector<std::string> lines;
auto strsplit_view = std::ranges::views::split(';') | std::ranges::views::transform([](auto &&rng)
{ return std::string_view(&*rng.begin(), std::ranges::distance(rng)); });
auto filesplit_view = lines |
std::ranges::views::transform([&](auto &&line)
{ return line | strsplit_view; });
for (auto line : filesplit_view)
{
do
{
print(line);
} while (std::ranges::next_permutation(line).found)
}
}
Is there a way of incorporating permutations into the view itself, or do I have to perform a separate loop like shown above?
The current code does not work on lines, what do I have to do in order to pass line into ranges::next_permutation in this case?
Error output:
no matching function for call to ‘std::basic_string_view<char>::basic_string_view(std::ranges::transform_view<std::ranges::split_view<std::ranges::ref_view<std::__cxx11::basic_string<char> >, std::ranges::single_view<char> >, main()::<lambda(auto:18&&)> >&)’
89 | } while (std::ranges::next_permutation(std::string_view(line)).found)
First, you should not convert the split pieces into std::string_view, because it is non-modifiable, which makes it impossible to use next_permutation. You should return std::span<char>.
Second, filesplit_view is a range whose elements are range adaptors. You need to use a for loop to traverse these range adaptors to get the actual split pieces.
#include <algorithm>
#include <ranges>
#include <string>
#include <vector>
int main() {
std::vector<std::string> lines;
auto strsplit_view =
std::views::split(';') | std::views::transform([](auto rng) {
return std::span(rng);
});
auto filesplit_view = lines |
std::views::transform([&](auto&& line) { return line | strsplit_view; });
for (auto adaptor : filesplit_view) {
for (auto line : adaptor) {
do {
// ...
} while (std::ranges::next_permutation(line).found);
}
}
}