Modes (was unbounded_string)

["Andrew Carroll" <andrew@carroll-tech.net>]

>>For all other types, the compiler chooses the parameter 
>>mode best suited to the type. 
Great!!!  SIGN ME UP!!!  But...is it possible that the compiler 
doesn't get it right?  What would I need to do if I found that
the compiler didn't get it right in my testing?  I'm guessing
that you will say, "specify the mode".

package x is
type x;
type xptr is access x;
type x is tagged limited record
 head: nodeptr; 
 something: unbounded_string;
end record;

--creates a new node to put into the 'head' list.
--new node is created from information in token.
--token has nothing to do with the 'something' variable
--declared in the record above.
procedure add(this: xptr; token: unbounded_string); 

end x;

So, with the above code "example", xptr is passed as an 'in'
or 'in out' mode at the add procedure?  

Are you saying that I should use just x and not xptr as the
parameter so that the compiler will choose the correct mode?
If so, you recommend it because of deallocation issues?


On to strings...
>> Basically, you have reinvented the wheel. What you have is 
>> Unbounded_String, but with its guts hanging out all over the place, 
>> instead of using information hiding as a software engineer should, and 
>> as Ada.Strings.Unbounded does.
[snip]
>> The "Ada Way" / "Ada idiom"

Is there something in the code below that I missed about information 
hiding?  

Temp: gnat.os_lib.String_Access;
...
Temp := gnat.os_lib.getenv("QUERY_STRING");
...
---------------------------------------
-- ready to use Temp for something else
---------------------------------------
Temp := gnat.os_lib.getenv("SOME_OTHER_VARIABLE");

Considering the code above, what is the "Ada idiom" to "resize" a String
without pointers and dynamic allocation?  In other words; what "Ada 
idiom" code would you write to do the same thing I did, without pointers
and dynamic allocation?  You don't have to write the code, a good 
reading reference would be okay.

Thanks!