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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Negative float problem
Date: 01 Nov 2005 19:13:36 -0500
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2005-11-01T19:13:36-05:00
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"Martin Dowie" <martin.dowie@baesystems.com> writes:

> Robert A Duff wrote:
> > I think Dmitry's point is that overload resolution in Ada is both
> > bottom-up and top-down.  It's simpler in C++ -- just bottom-up.
> >
> >     type Color is (Red, Blue);
> >     type Traffic_Light is (Green, Amber, Red);
> >     procedure P(Param: Color);
> >
> >     P(Red);
> >
> > This is legal in Ada.  The compiler knows which Red is meant
> > based on the expected type for Param.  Similar things are
> > illegal in C++ (I think -- am I right?).
> 
> Yup, you can't have overloaded enumeration values - I guess because they are
> really just 'int', so which one would you mean?

Sorry.  My post was confusing.

In Ada, enum lits are parameterless functions.  So the corresponding
thing in C++ would be parameterless functions.  So pretend my example
was something like:

    function Red return Color;
    function Blue return Color;
    function Green return Traffic_Light;
    function Amber return Traffic_Light;
    function Red return Traffic_Light;

    procedure P(Param: Color);

    P(Red);

That sort of thing works fine in Ada, but C++ doesn't like it.

I wasn't talking about the difference between enums in C++ versus Ada.
I was talking about the difference in overload resolution rules.
Namely that the result type of a function call is used to resolve
in Ada, but not in C++.  (And by the way Ada has this weird idea
that enum lits are functions.)

- Bob