Re: Ada Popularity: Comparison of Ada/Charles with C++ STL (and Perl)

From: Dmitry A. Kazakov (mailbox_at_dmitry-kazakov.de)
Date: 10/04/04 

Date: Mon, 4 Oct 2004 15:21:53 +0200

On Mon, 04 Oct 2004 12:16:58 GMT, Matthew Heaney wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
>
>> It is because they are not arrays. But why an ordered list should not
>> implement an array interface? In my view it should, making the above
>> legal for lists.
>
> Stop obsessing about syntax.

Aha, but semantically that all is just a Turing machine. So yes, I am
obsessed with syntax. (:-))

> If you want a consistent interface for
> containers, you have that in AI-302 (but of course it's not an "array"
> interface):
>
> procedure Op (Container : <container's type>) is
> C : Cursor := First (Container);
> begin
> while Has_Element (C) loop
> Process (C); --or Process (Element (C))
> Next (C);
> end loop;
> end Op;
>
> Actually, if you intend on iterating over all the elements in a
> container, the passive iterator is preferred:
>
> procedure Op (Container : <containers's type> is
> begin
> Container.Iterate (Process'Access);
> end;
>
> If you have an array type, then you can give it a container-like
> interface for the purpose of binding an array object to a generic
> algorithm. I showed how to do this in an earlier post.

This is what I think the wrong way is - to use Ada's arrays like STL
containers, instead of the reverse. You will probably agree that iteration
is a fundamental programming pattern. As such, it IMO deserves a separate
language construct rather than being hidden in a subroutine call.

>> I do! I hate implicit iterators, I prefer loops where
>> possible. Especially, because exit conditions, nested iterations,
>> exception handling become visible.
>
> If you intend on traversing every element in the container, then use a
> passive iterator. It's more efficient, and less error-prone.
>
> If you have exit conditions, then go ahead and use an active-iterator
> style loop.

Just compare:

 declare
    C : Cursor := First (Container);
 begin
    while Has_Element (C) loop
       Process (Element (C));
       Next (C);
    end loop;
 end;

with

 for C in Container'Range loop
    Process (Container (C));
 end loop;
 
You have to know about Cursor, First, Has_Element, Element and Next only to
call Process on each element of a container!

[ Don't even try to tell me that First is like 'First etc. Because, being
obsessed with syntax, I will reply that then it should be named 'First!
(:-)) ]

>> [ Ranting: 40 years spent in developing readable, safe, well-structured
>> language constructs, only to replace them with nested function calls a la
>> Lisp? ]
>
> This is a specious comparison.

I tried hard... (:-)) 

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

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