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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: STRING length
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Date: Wed, 15 Nov 2006 02:17:48 +0100
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Date: 2006-11-15T02:17:48+01:00
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markww writes:
> Thanks Georg, that looks to be exactly what I need. I do have a problem
> '#including', or, 'withing' rather unbounded string.
> Now the head of my source file looks like:
>
>     with Ada.Text_IO, Ada.Integer_Text_IO, Ada.Strings.Unbounded;
>     use Ada.Text_IO, Ada.Integer_Text_IO;
>
> which is alright but as soon as I try:
>
>     use Ada.Strings.Unbounded;
>
> the compiler gives me a bunch of errors, it seems to conflict with
> Text_IO / Integer_Text_IO? Seems like all my previous calls to Put()
> now became invalid. I'm not familiar with Ada but with C++ and
> understand namespace collisions, is the same thing going on here?

In theory, a use clause may make subprogram calls ambiguous and thus
illegal, but I don't think that's your problem here, because
Ada.Strings.Unbounded does not contain any Put subprogram that might
collide with those in Ada.Text_IO or Ada.Integer_Text_IO.

Instead, I think that your problem stems from the the use clause
making the following operators directly visible (from ARM A.4.5):

 15.      function "&" (Left, Right : in Unbounded_String)
             return Unbounded_String;

 16.      function "&" (Left : in Unbounded_String; Right : in String)
             return Unbounded_String;

 17.      function "&" (Left : in String; Right : in Unbounded_String)
             return Unbounded_String;

 18.      function "&" (Left : in Unbounded_String; Right : in Character)
             return Unbounded_String;

 19.      function "&" (Left : in Character; Right : in Unbounded_String)
             return Unbounded_String;

so now you're constructing unbounded strings by concatenating strings
and unbounded strings, and passing them to Ada.Text_IO.Put, which is
of course illegal.

You should convert the unbounded strings to regular strings before
passing them to Ada.Text_IO.Put, like so:

with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;
with Ada.Text_IO;
procedure Foo is
   S : Unbounded_String := "Hello" & To_Unbounded_String (", world!");
   -- calls Ada.Strings.Unbounded."&" which is directly visible
begin
   Ada.Text_IO.Put (To_String (S)); -- convert and print
end Foo;

HTH

-- 
Ludovic Brenta.