boost::format with type-safe C-style format strings

format.cpp

#include "boost/format.hpp"
#include <string>
#include <utility>

inline auto fmt_r(boost::format & format) -> boost::format & {return format;}

template<typename T, typename... Args>
auto fmt_r(boost::format & format, T && val, Args &&... args) -> boost::format & {
    return fmt_r(format % std::forward<T>(val), std::forward<Args>(args)...);
}

template<typename... Args>
auto fmt(const std::string & format_str, Args &&... args) -> std::string {
    boost::format format(std::move(format_str));
    fmt_r(format, std::forward<Args>(args)...);
    return format.str();
}