Iterator Syntax [was: Re: STL in Ada95]

[Jeff Carter <carter@spam.innocon.com>]

Brian Rogoff wrote:
> 
> John Volan wrote:
...
> >   generic
> >     type Iterator_Type is private;
> >     type Item_Type is private;
> >     with procedure Advance (Iterator : in out Iterator_Type);
> >     with function Get_Item (Iterator : in Iterator_Type) return
> > Item_Type;
> >     ... -- whatever other formals
> >   procedure Do_Whatever                     -- whatever the algorithm is
> >     (Start, Stop : in Iterator_Type; ... ); -- whatever parameters

I'm curious. What is the advantage of "exposed" iterators like these
over encapsulated iterators for a structure:

generic -- Iterate
   with procedure Action (Item : in out Element; Continue : out
Boolean);
procedure Iterate (Over : in Structure);

The most typical usage, in my experience, has been to process every
Element in the Structure. Stopping before the end is rare; skipping some
at the beginning is even rarer. Processing every Element is easy for the
client with an encapsulated iterator (even easier if you leave the
Continue parameter out of Action). The exposed iterator requires the
client to set up Start and Stop and provide appropriate Advance and
Get_Item operations.
-- 
Jeff Carter  PGP:1024/440FBE21
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