Visibility

[And838N@netscape.net]

>Why did you "with" and "use" ada.text_io, when your program doesn't 
>need them?  Elimination of this error solves the problem of visibility 
>of "count". 
Well, if I don't "with" ada.text_io I get the following message from
gnatmake.
iotest.adb:4:09: "put_line" is undefined
iotest.adb:4:09: possible missing with of Text_IO
iotest.adb:4:10: "put" is undefined
iotest.adb:4:10: possible missing with of Text_IO
hence, the reason I "withed" text_io.
 
>I could find no such statement on my copy of Cohen's book. 
Page 1039, Section A.2

>There is no such unit as "unbounded_text_io" in the Ada standard
>libraries. 
Hmmm...I have a "with" for Ada.strings.unbounded.text_io and the file 
in <libdirectory>/adainclude/a-suteio.ads (using gcc-lib) says
otherwise.  The package that has the Count function I am talking about
is ada.strings.unbounded.

According to Cohen and obviously GNAT, the Count variable in text_io
and the function with the same name from unbounded are visible in the
same place, and for some reason it, GNAT, does not "determine" or maybe
cannot determine which one to use by "signature".  To me, if anything,
GNAT should have said something to the effect that I was trying to
perform some sort of narrowing conversion rather than telling me that
it did not know which Count to use because of a visibility issue.

with
ada.strings.unbounded,
ada.text_io,
ada.strings.maps;

use
ada.strings.unbounded,
ada.text_io,
ada.strings.maps;

procedure visibilitytest is
        astring: string := "hello world";
        somenumber: integer;
begin
        put_line(astring);
        somenumber := count(to_unbounded_string(astring), to_set(' '));
        put_line(Integer'image(somenumber));
end visibilitytest;

This code does not compile first because of a visibility issue.  The
compiler output, gnatmake visibilitytest.adb -gnatf, yields:
adagcc -c -gnatf visibilitytest.adb
visibilitytest.adb:18:23: "count" is not visible
visibilitytest.adb:18:23: multiple use clauses cause hiding
visibilitytest.adb:18:23: hidden declaration at a-textio.ads:66
visibilitytest.adb:18:23: hidden declaration at a-strunb.ads:217
visibilitytest.adb:18:23: hidden declaration at a-strunb.ads:211
visibilitytest.adb:18:23: hidden declaration at a-strunb.ads:205
gnatmake: "visibilitytest.adb" compilation error

The fix is to specify which one to use on line 18.
somenumber := ada.strings.unbounded.count(to_unbounded_string(as
tring), to_set(' '));.  To me, GNAT should be able to resolve which
count to use because the count in ada.strings.unbounded is a function
and count in ada.text_io is a type.  Not to mention the function
returns (or is of type) Natural, not count.

The answer to my question was in Cohen's book, chapter 10.  The 
rules for the "with" clause and packages are to make a large 
number of files easier to manage and to make it clear to the reader
what is going on with any particular file.  The "with" clause just
makes "stuff" visible; it is up to the programmer/engineer to specify
or clarify, by using an expanded name, what facilities they are "use"
ing from a particular package.  Thus, GNAT's compiler message tells
me not that GNAT can't determine which count to use but that I need
to specify, for future readers, which count I needed.  In doing so
,if I am searching for count, I narrow the search to the exact 
package I need to look in for the count I "used". 

I'll be looking into Elaboration next.  It sounds to me like the 
elaboration of a package is like the instantiation of a C++ class.
If that's true, then I should be able to have multiple elaborations
of a package that all have different values for their data members.
And if that is true, then I've been using the package the wrong way.

Thanks for the help all.

Andrew

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