Re: Enumeration literals and their associated functions

["Randy Brukardt" <randy@rrsoftware.com>]

"Niklas Holsti" <nobody@nowhere.fi> wrote in message
news:D6Q5f.3855$Yx5.800@reader1.news.jippii.net...
> Maciej Sobczak wrote:
> > Hi,
> >
> > <http://www.adaic.org/standards/95aarm/html/AA-3-5-1.html>, paragraph 6
> > states that for each enumeration literal specification there is an
> > appropriate parameterless function declated.
> >
> >    type Color is (RED, GREEN, BLUE);
> >
> > ...
> > If instead "RED" above is considered to be a literal, then what's the
> > sense of having an associated function at all?
>
> I believe that the LRM defines enumeration literals as functions
> because this automatically defines their overloading. That is, you
> can have another enumeration type that also has the literal RED (a
> synonym), yet overloading lets the compiler resolve which RED is
> meant, by the context.

Right. The classic example is:

    type Base is (Bin, Oct, Dec, Hex);
    type Month is (Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov,
Dec);

Both enumerations have literals Oct and Dec. If these were treated as
objects, that would be illegal. So the language treats them as intrinsic
functions instead. Then
   This_Month : Month := Oct;
works, because the standard overloading rules apply.

Practically, you can just think of them as overloaded literals. It probably
makes more sense that way. The definition as a function is primarily to make
the language rules more consistent (and simpler); it's not some sort of
important feature.

                         Randy.