musingstudio

One of many neat features in C++11 is the introduction of ‘enum class’ – this addresses problems arising from enum declarations such as scoping (the enum cases leak in the same scope as the enum type) and implicit conversion to integer. See Stroustrup’s C++11 FAQ for more details.

However, in the papers that motivated the new language feature (N1513 and N2347) they discuss the current workarounds for C++03. One such workaround is to define a class to represent the enum type – it’s much more verbose than the new C++11 feature, but it solves the scoping and conversion issues.

// Header file
class Weekday
{
private:
  // Note that the private enum cases have underscores to differentiate
  // from the public cases
  typedef enum Weekday_ { Mon_, Tues_, Wed_, Thurs_, Fri_, Sat_, Sun_ };
  Weekday_ value_;

public:
  static const Weekday Mon, Tues, Wed, Thurs, Fri, Sat, Sun;
  explicit Weekday( const Weekday_& value ) : value_( value ){}

  bool operator<( const Weekday& rhs ) const { return this->value_ < rhs.value_; }
  bool operator==( const Weekday& rhs ) const { return this->value_ == rhs.value_; }
  bool operator!=( const Weekday& rhs ) const { return !(this->operator==(rhs)); }
};

// Source file
// Definitions for the public Weekday instances 
// in terms of the private enum
const Weekday Weekday::Mon( Mon_ );
const Weekday Weekday::Tues( Tues_ );
const Weekday Weekday::Wed( Wed_ );
const Weekday Weekday::Thurs( Thurs_ );
const Weekday Weekday::Fri( Fri_ );
const Weekday Weekday::Sat( Sat_ );
const Weekday Weekday::Sun( Sun_ );

That’s it – I’ve been using this recently and it works pretty well. I also added a “to_int()” member and a static “from_int()” member to explicitly convert bewteen the enum class and integers – the implementation is simply a switch over the enum cases.