split_span.h

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#pragma once

 
#include <array>
#include <cstddef>
#include <span>
 
namespace pixie {

template <class T>
class SplitSpan {
 public:
  using span_type = std::span<T>;
  using const_iterator = typename std::array<span_type, 2>::const_iterator;

  constexpr SplitSpan() = default;

  constexpr explicit SplitSpan(span_type segment)
      : segments_{segment, {}}, segment_count_(segment.empty() ? 0 : 1) {}

  constexpr SplitSpan(span_type first, span_type second) {
    if (first.empty()) {
      first = second;
      second = {};
    }
    segments_ = {first, second};
    segment_count_ = static_cast<std::size_t>(!first.empty()) +
                     static_cast<std::size_t>(!second.empty());
  }

  constexpr std::size_t size() const noexcept {
    return segments_[0].size() + segments_[1].size();
  }

  constexpr bool empty() const noexcept { return segment_count_ == 0; }

  constexpr std::size_t segment_count() const noexcept {
    return segment_count_;
  }

  constexpr const_iterator begin() const noexcept { return segments_.begin(); }

  constexpr const_iterator end() const noexcept {
    return segments_.begin() + static_cast<std::ptrdiff_t>(segment_count_);
  }
 
 private:
  std::array<span_type, 2> segments_{};
  std::size_t segment_count_ = 0;
};
 
}  // namespace pixie