Re: Unbounded Strings

[Craig Carey <research@ijs.co.nz>]

On Wed, 08 Oct 2003 18:46:18 GMT, Jeffrey Carter <spam@spam.com> wrote:
>Andrew Carroll wrote:
>> I did some experimenting, thanks to Cohen's book and persistance I found
Is that book online?
...
>All elementary types are passed by copy, regardless of the parameter mode. 
>All tagged and limited types are passed by reference, regardless of the 
>parameter mode. For all other types, the compiler chooses the parameter 
>mode best suited to the type.

Other candidates for the by-reference type include:
 * records with an aliased field
 * records with a field that is a type that is either Volatile or Atomic.

Once tagged is used, then a type can't be renamed without having to
rename all of its procedures which is adverse to my idea of a language
that ought provide strong type checking. No procedures beneath/above this
line.

Use of the limited reserved word can stop the assigning of records which
can be too inconvenient.

This is what I do: use aliased fields, and if it results in a few extra
procedures, maybe they get inlined correctly:

   ---------
   type UST is Ada.Strings.Unbounded.Unbounded_String;

   type UST_Rec is tagged
      record
         Val   : aliased UST;
      end record;

   type UST_Ptr is access constant UST;

   function Access_To (X : UST_Rec) return UST_Ptr;
   ---------

By some method, the function returns a pointer to the field.

So the parameter is aliased and the term by-reference is not getting
properly explained when there is no consideration of what it means when
there is background garbage collecting.




Craig Carey