Support for ranges

[gnzlbg]

Add support for printing ranges. Ideally:

std::initializer_list<int> a = {0, 2, 3, 4};
print("range: \"{r{}, }\"\n", a);
print("range: \"{r{}| }\"\n", a);
std::initializer_list<std::initializer_list<int>> a = { {0, 1}, {2, 3}, {4}};
print("range: \"{r{r{}, }| }\"\n", a);

would print

range "0, 2, 3, 4"
range "0 | 2 | 3 | 4"
range "0, 1 | 2, 3 | 4"

This would require a new format specifier, e.g. r, followed by a format specifier for the range element and a separator string: r{}sep. Note that r{r{}sep0}sep1 allows dealing with ranges of ranges.
A definition of Range, e.g., anything that can be called with non-member begin and end.

[vitaut]

Interesting idea. It should be possible to do via an extension mechanism:

#include <initializer_list>
#include "format.h"

namespace fmt {
template <typename Char, typename T>
void format(fmt::BasicFormatter<Char> &f, const Char *&format_str,
            std::initializer_list<T> values) {
  fmt::BasicWriter<Char> &writer = f.writer();
  for (const auto &value: values)
    writer << value;
}
}

int main() {
  std::initializer_list<int> a = {0, 2, 3, 4};
  fmt::print("range: \"{}\"\n", a);
}

This prints range: "0234" without any separators, but it is possible to parse the format string and write in the format you suggest.

[gnzlbg]

Cool I'll give it a try!

[vitaut]

Looks like this feature can be implemented on top of existing API without changes to the core library, so I'm going to close this. Feel free to reopen if this is not the case.