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From: mheaney@on2.com (Matthew Heaney)
Newsgroups: comp.lang.ada
Subject: Re: using charles library
Date: 27 May 2003 08:05:47 -0700
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Jeffrey Carter <spam@spam.com> wrote in message news:<3ED24C46.6080208@spam.com>...
> Roman V. Isaev wrote:
> > 
> >    I wonder is there any package easier to use? I only want two
> > functions, something like store(key,value) and lookup(key), that's
> > all, without 20+ string declaration voodoo... Grrrrr. I miss perl's
> > associative arrays.

Your problem is a consequence of the fact that the intended element
type, String, is indefinite.  Most container libraries in Ada
--including Charles-- require container elements to be definite, with
some kind of constraint.  That's why the generic formal type looks
like this:

generic
  type Element_Type is private;
package GP is ...;

Note that this is the case even for built-in array types: type String
cannot be an array component subtype directly.

Had you chosen a simpler type, as Integer or Float, then you would
have had fewer difficulties instantiating the component.

If you need to use type String as a container element, then you need
some kind of wrapper class, either Ada.Strings.Unbounded or
Charles.Strings.Unbounded, that is itself definite.

To store a key/element pair in the map, use Insert:

  Insert (Map, Key, Element);

That operation is overloaded to return an iterator that designates the
pair:

  Insert (Map, Key, Element, Iterator);

It's overloaded again to return a Success parameter, which allows the
insertion to be conditional (insert fails if key is already in the
map):

  Insert (Map, Key, Element, Iterator, Success);


To lookup a key/value pair, just use the Find operation:

procedure Op (Map : Map_Subtype) is
  I : Iterator_Type := Find (Map, Key);
begin
  if I /= Back (Map) then
    declare
      E : Element_Type := Element (I);
      --or E : Element_TYpe renames To_Access (I).all;
    begin
      ...
    end;
  end if;
end;

It wasn't clear from your original example why you were using
Ada.Strings.Unbounded, if you were using Charles.Strings.Unbounded as
the element type.

Drop me a line if any of this isn't clear.

Matt