Variable.h

#pragma once
 
#include <cstddef>
#include <functional>
#include <iosfwd>
#include <string>
#include <vector>
 
namespace delpi {

class Variable {
 public:
  using Id = std::size_t;
 
  static const Id dummy_id;  

  Variable() : id_{dummy_id} {}
  explicit Variable(std::string name);
  explicit Variable(Id id);

  [[nodiscard]] bool is_dummy() const { return id_ == dummy_id; }
  [[nodiscard]] Id id() const { return id_; }
  [[nodiscard]] const std::string &name() const { return names_[id_ + 1]; }

  [[nodiscard]] bool equal_to(const Variable &o) const noexcept { return id_ == o.id_; }
  [[nodiscard]] bool less(const Variable &o) const noexcept { return id_ < o.id_; }
  [[nodiscard]] size_t hash() const noexcept { return std::hash<Id>{}(id_); }
 
  Variable operator+() const { return *this; }
 
 private:
  static std::vector<std::string> names_;  
  static Id GetNextId();
 
  Id id_{};  
};
 
std::ostream &operator<<(std::ostream &os, const Variable &var);
}  // namespace delpi
 
template <>
struct std::hash<delpi::Variable> {
  size_t operator()(const delpi::Variable &v) const noexcept { return v.hash(); }
};
 
template <>
struct std::less<delpi::Variable> {
  bool operator()(const delpi::Variable &lhs, const delpi::Variable &rhs) const noexcept { return lhs.less(rhs); }
};
 
template <>
struct std::equal_to<delpi::Variable> {
  bool operator()(const delpi::Variable &lhs, const delpi::Variable &rhs) const noexcept { return lhs.equal_to(rhs); }
};
 
#ifdef DELPI_INCLUDE_FMT
 
#include "delpi/util/logging.h"
 
OSTREAM_FORMATTER(delpi::Variable);
 
#endif