Re: SIGada Conference

["Robert I. Eachus" <rieachus@comcast.net>]

Stephen Leake wrote:

> Since the ARG people are _very_ smart, and _very_ motivated to
> conserve implementors time, I suspect you are wrong :). Personally, I
> think Java-style interfaces will let me do things I simply cannot do
> now.

Thanks for the compliment.  But I think everyone should be aware that we 
don't care whether or not a feature is "necessary."  What we really 
agonize about is how to make programming in Ada easier and make it more 
likely that Ada programs will satisfy all the "ilities."

The interfaces proposal allows a style of multiple inheritance that is 
currently not well supported in Ada.  Wonderful.  But the reason that it 
is a slam dunk that it will be in there, even if it does result in 
adding a new reserved word, is that it makes in much easier in many 
cases for a programmer to document what he is really trying to do.

It is possible to make fancy use of generics and dispatching so that you 
can have one specification matched by different bodies.  But the fact 
that different members of a class are handled in very different ways is 
hidden in the structure of the program.  Interfaces allow a programmer 
to say he is doing just that, and doing it intentionally.

For example you can have an indexed list type that calls different sort 
routines, hash table, radix sort, b-tree, etc. depending on the type of 
the index.  With interfaces the "documentation" of this occurs where the 
interface is implemented for a specific type of index, rather than where 
the index types are declared.  (And you don't need to manufacture a 
tagged parent type to make it work.)

-- 
                                           Robert I. Eachus

"The war on terror is a different kind of war, waged capture by capture, 
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