Re: The simple Image issue

[Georg Bauhaus <rm.dash-bauhaus@futureapps.de>]

On 31.08.11 18:43, Adam Beneschan wrote:
> On Aug 31, 9:34 am, Georg Bauhaus<rm.dash-bauh...@futureapps.de>
> wrote:
>
>>>> True when there is an object; but what about
>>
>>>>    (some expression)'Value ?
>>
>>> Use T(expression)'Value when you must.
>>
>> Even so,
>>
>>   X := T'(if condition then
>>            1.2
>>           else
>>            3.5)'Value;
>
> Hang on... doesn't the argument of 'Value need to be a string?  I
> think this conversation took a wrong turn up there---you all meant
> 'Image, right?

OK, yes, I was too, uh, quick, I meant "1.2" and "3.5 and so on.

I'll like the polymorphing Value function best.
But Dmitry mentions objects as the result of parsing.

To me, this seems more about persistent objects than about
something that assists newcomers with quickly writing values
(of numbers and of enums) in and out.  Isn't persistence better
served by 'Output and 'Input?

Isn't part of the argument about the gap between untagged and
tagged types?


Rather than changing 'image and 'value, some Ada effort, IMHO,
is better directed towards the creation of a flexible, portable
tracing package, if tracing seems to dominate the use cases of
quick 'Img.  Would it work?  Starting from:

   procedure P ...
     X : ...
   begin
     ...
     put_line (current_error, "In P, value X is="
                             & T'image(X));

I'd imagine a portable compiler magic package:

   package Source_Info is ...


   trace : Source_Info.T;

   Trace.Set_Output (Current_Error);

   procedure P ...
     X : ...
   begin
     ...
     Trace.Debug ("value X is=", X);
  
I am assuming that the compiler will be determining procedure
P's full name, and can either infer the type of X and then select
or synthesize a suitable transformation function, or will ask the user
for assistance as necessary. The output format can be configured, etc.

I cannot imagine a project where such a package would not be
used.

Maybe it is irritating that there should be procedures that
have more magic than others.  Some syntax should help lessen the
surprise.

A magic trace package is even easier to use for newcomers and
programmers alike. It is also portable, unlike 'Img.

Fancy words like "compiler assisted code injection" etc. will
allow marketing.


Come to think of it, Eiffel has a reserved word, "debug",
not sure about compiler magic for source info.