atom.hpp

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#ifndef ATOM_HPP
#define ATOM_HPP

#include "token.hpp"

class Atom {
public:

  Atom();

  Atom(double value);

  Atom(const std::string & value);

  Atom(const Token & token);

  Atom(const Atom & x);

  Atom & operator=(const Atom & x);

  ~Atom();

  bool isNone() const noexcept;

  bool isNumber() const  noexcept;

  bool isSymbol() const noexcept;

  double asNumber() const noexcept;

  std::string asSymbol() const noexcept;

  bool operator==(const Atom & right) const noexcept;

private:

  // internal enum of known types
  enum Type {NoneKind, NumberKind, SymbolKind};

  // track the type
  Type m_type;

  // values for the known types. Note the use of a union requires care
  // when setting non POD values (see setSymbol)
  union {
    double numberValue;
    std::string stringValue;
  };

  // helper to set type and value of Number
  void setNumber(double value);

  // helper to set type and value of Symbol
  void setSymbol(const std::string & value);
};

bool operator!=(const Atom &left, const Atom & right) noexcept;

std::ostream & operator<<(std::ostream & out, const Atom & a);

#endif