Re: Problem with Enumaration and visibility

[Ted Dennison<dennison@telepath.com>]

In article <slrn9v4uqg.h34.randhol+abuse@kiuk0156.chembio.ntnu.no>, Preben
Randhol says...
>I have defined a Enumarated type in a package called setup. I need to
>use this in another package called Examine. If I do as below, I get this
>error from GNAT:
>
>   examine.adb:130:17: operator for type "Method_Enum_Type" defined at
>   setup.ads:64 is not directly visible
>
>   examine.adb:130:17: use clause would make operation legal
>   examine.adb:130:47: "Spell" is not visible
>   examine.adb:130:47: non-visible declaration at setup.ads:64
..
>if I add "use Setup;" in the Start procedure it works. Why do I have
>to do this? Is there a different way without using use. I'm just
>asking to understand how this works with enumarated types.

First off, this is a *really* basic issue, which would take a good deal of
exposition to explain properly. I suggest you read an Ada book rather than have
people here try to get into it. Chapter 2 of John English's book goes into this,
if you don't have your own dead-tree book handy. See
http://www.it.bton.ac.uk/staff/je/adacraft/ch02.htm . Go read that, then come
back here. I'll wait...

Now: Yes there is another way. Some (including myself) would argue that its is
in fact the proper way to do it. What you do is prepend the package name in
front of the name of every object in that package that you reference. For
instance, in examine.adb, "Spell" would become "Setup.Spell". The second thing
you will need to do is change that "use" clause to a "use type" clause for the
type in question (Setup.Method_Enum_Type). That gives you direct visibility to
built-in infix operators like "=".

I highly suggest all newbies use this approach rather than just doing a "use"
clause for the whole package, as it trains you to think about where you are
getting things from. One you become proficient with Ada, you can decide for
yourself if you need to continue working that way.

---
T.E.D.    homepage   - http://www.telepath.com/dennison/Ted/TED.html

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