// In header: <boost/log/attributes/mutable_constant.hpp>
template<typename T> 
class mutable_constant<T, void, void, void> : public attribute {
public:
  // types
  typedef T value_type;  // The attribute value type. 
  // member classes/structs/unions
  // Factory implementation.
  class impl : public attribute::impl {
  public:
    // construct/copy/destruct
    explicit impl(value_type const &);
    explicit impl(value_type &&);
    // public member functions
    virtual attribute_value get_value();
    void set(value_type const &);
    void set(value_type &&);
    value_type get() const;
  };
  // construct/copy/destruct
  explicit mutable_constant(value_type const &);
  explicit mutable_constant(value_type &&);
  explicit mutable_constant(cast_source const &);
  // public member functions
  void set(value_type const &);
  void set(value_type &&);
  value_type get() const;
  // protected member functions
  impl * get_impl() const;
};