Re: Efficient Enum Access...

On Apr 25, 11:48 am, Thomas Lehmann <t.lehm...@[EMAIL PROTECTED]
> wrote:
> How can I check wether a given value is
> contained by a given enum?

For enums for which the integer values are not significant,  I often
do something similar to:

enum color
{
   red, green, blue,
   // add more here
   color_cnt // keep me last
};

void f(int raw_color)
{
   if (raw_color < 0 || raw_color >= color_cnt)
      throw std::runtime_error("Unexpected data.");

   color c = static_cast<color>(raw_color);

   // ...
}

It seems like that 'if' range assertion could be made to work in one
of the enum_cast function templates suggested by others, even without
specialization, if one were willing to commit to a little discipline
in naming:

struct color {
   enum enum_type // always named this
   {
     red, green, blue,
     // add more here
     count_of_enumerators // always named this
   };
};

template <class enum_wrapper_T, class conv_to_integral_T>
typename enum_wrapper_T::enum_type enum_cast(conv_to_integral_T
raw_val)
{
   int n = raw_val;

   if (n < 0 || n >= enum_wrapper_T::count_of_enumerators)
      throw std::runtime_error("Unexpected data.");

   return static_cast<enum_wrapper_T::enum_type>(n);
}

This has a side effect (one which I like) of hiding the enum
identifiers inside the struct color:

void f(int raw_color)
{
   switch (enum_cast<color>(raw_color))
   {
   case color::red:   /* ... */ break;
   case color::green: /* ... */ break;
   case color::blue:  /* ... */ break;
   //default: Really can't happen if cases cover all enumerators.
   }
}

- Marsh

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