string_view.h

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#ifndef XGBOOST_STRING_VIEW_H_
#define XGBOOST_STRING_VIEW_H_
#include <xgboost/logging.h> // CHECK_LT
#include <xgboost/span.h> // Span
 
#include <algorithm> // for equal, min
#include <cstddef> // for size_t
#include <iterator> // for reverse_iterator
#include <ostream> // for ostream
#include <string> // for char_traits, string
 
namespace xgboost {
struct StringView {
 private
 using CharT = char;
 using Traits = std::char_traits<CharT>
 CharT const* str_{nullptr};
 std::size_t size_{0};
 
 public
 using value_type = CharT; // NOLINT
 using iterator = const CharT*; // NOLINT
 using const_iterator = iterator; // NOLINT
 using reverse_iterator = std::reverse_iterator<const_iterator>; // NOLINT
 using const_reverse_iterator = reverse_iterator; // NOLINT
 
 public
 constexpr StringView() = default;
 constexpr StringView(value_type const* str, std::size_t size) : str_{str}, size_{size} {}
 StringView(std::string const& str) : str_{str.c_str()}, size_{str.size()} {} // NOLINT
 constexpr StringView(value_type const* str) // NOLINT
 : str_{str}, size_{str == nullptr ? 0ul : Traits::length(str)} {}
 
 [[nodiscard]] value_type const& operator[](std::size_t p) const { return str_[p]; }
 [[nodiscard]] explicit operator std::string() const { return {this->c_str(), this->size()}; }
 [[nodiscard]] value_type const& at(std::size_t p) const { // NOLINT
 CHECK_LT(p, size_);
 return str_[p];
  }
 [[nodiscard]] constexpr std::size_t size() const { return size_; } // NOLINT
 [[nodiscard]] constexpr bool empty() const { return size() == 0; } // NOLINT
 [[nodiscard]] StringView substr(std::size_t beg, std::size_t n) const { // NOLINT
 CHECK_LE(beg, size_);
 std::size_t len = std::min(n, size_ - beg);
 return {str_ + beg, len};
  }
 [[nodiscard]] value_type const* c_str() const { return str_; } // NOLINT
 
 [[nodiscard]] constexpr const_iterator cbegin() const { return str_; } // NOLINT
 [[nodiscard]] constexpr const_iterator cend() const { return str_ + size(); } // NOLINT
 [[nodiscard]] constexpr iterator begin() const { return str_; } // NOLINT
 [[nodiscard]] constexpr iterator end() const { return str_ + size(); } // NOLINT
 
 [[nodiscard]] const_reverse_iterator rbegin() const noexcept { // NOLINT
 return const_reverse_iterator(this->end());
  }
 [[nodiscard]] const_reverse_iterator crbegin() const noexcept { // NOLINT
 return const_reverse_iterator(this->end());
  }
 [[nodiscard]] const_reverse_iterator rend() const noexcept { // NOLINT
 return const_reverse_iterator(this->begin());
  }
 [[nodiscard]] const_reverse_iterator crend() const noexcept { // NOLINT
 return const_reverse_iterator(this->begin());
  }
};
 
inline std::ostream& operator<<(std::ostream& os, StringView const v) {
 for (auto c : v) {
 os.put(c);
  }
 return os;
}
 
inline bool operator==(StringView l, StringView r) {
 if (l.size() != r.size()) {
 return false;
  }
 return std::equal(l.cbegin(), l.cend(), r.cbegin());
}
 
inline bool operator!=(StringView l, StringView r) { return !(l == r); }
 
inline bool operator<(StringView l, StringView r) {
 return common::Span<StringView::value_type const>{l.c_str(), l.size()} <
 common::Span<StringView::value_type const>{r.c_str(), r.size()};
}
 
inline bool operator<(std::string const& l, StringView r) { return StringView{l} < r; }
 
inline bool operator<(StringView l, std::string const& r) { return l < StringView{r}; }
} // namespace xgboost
#endif // XGBOOST_STRING_VIEW_H_