optional_last_value.hpp

#ifndef SIGNALS_OPTIONAL_LAST_VALUE_HPP
#define SIGNALS_OPTIONAL_LAST_VALUE_HPP
#include <optional>
#include <utility>
 
namespace sig {
 
 
template <typename T>
class Optional_last_value {
   public:
    using Result_type = std::optional<T>;
 
   public:
    template <typename InputIterator>
    auto operator()(InputIterator first, InputIterator last) const
        -> Result_type
    {
        if (first == last)
            return {std::nullopt};
        auto temp = T();
        while (first != last) {
            temp = *first;
            ++first;
        }
        return {std::move(temp)};
    }
};
 
 
template <>
class Optional_last_value<void> {
   public:
    using Result_type = void;
 
   public:
    template <typename InputIterator>
    auto operator()(InputIterator first, InputIterator last) const
        -> Result_type
    {
        while (first != last) {
            *first;
            ++first;
        }
    }
};
 
}  // namespace sig
#endif  // SIGNALS_OPTIONAL_LAST_VALUE_HPP