Re: Wrapping enums

  posted:


I've copy-pasted something I posted recently. (I'd give a link to Google
Groups but the post isn't available on Google Groups -- only about 80% of
Usenet posts are available on Google Groups).

Given the following enumeration type:

enum Day {
     Monday,Tuesday,Wednesday,Thursday,
     Friday,Saturday,Sunday
};

The names, "Day" and also "Monday", "Tuesday", and so forth are all in
the
same scope. This can be unsatisfactory if you later try to define another
enum:

     enum WorkDay {
         Monday,Tuesday,Wednesday,Thursday,Friday
     };

or if try to define an object:

     int Tuesday = 5; /* Name clash! */

I've seen people wrap their enum's in a namespace... but that doesn't
work
out too well (try passing a namespace to a function!). I set about trying
to
find a way to use an enum exactly how I want to, and here's what I've got
so
far. Instead of having:

enum Day { Monday, Tuesday, Wednesday, Thursday,
     Friday, Saturday, Sunday };

I have:

struct Day {

     enum TheEnumWithin{

         Monday,Tuesday,Wednesday,Thursday,
         Friday,Saturday,Sunday

     } data;

     Day() {}

     Day( TheEnumWithin const tew ) : data(tew) {}

     operator TheEnumWithin&() { return data; }
};

The aim is to use it just like a normal enum, but without the name
clashes.
Sample usage:

bool SomeFunc1( Day d )
{
     switch (d)
     {
     case Day::Monday:
     case Day::Wednesday:
     case Day::Friday:

         return true;

     default:

         return false;
     }
}

int main()
{
     Day d;

     d = Sunday; /* Won't work! */

     d = Day::Sunday;

     d = 3; /* Won't work! */

     d = Day::TheEnumWithin(3);

     SomeFunc1( d ); /* Can pass to function */
}

I only started writing the code within the last half hour, so it's by no
means a finished product! One problem I've just encoutered is dealing
with
const objects of it; specifically, I want to add the following member
function:

     operator const TheEnumWithin&() const { return data; }

But then this conflicts with:

     operator TheEnumWithin&() { return data; }

Any thoughts?

(If you ask me, there should be a new kind of structure added to C++,
some
sort of enclosed enum.)

I might even use some sort of macro trickery so that I can just write:

EnclosedEnum Day {
     Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday
};

-Tom?s

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