Re: Manifesto against Vector

[Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>]

On Thu, 06 May 2004 15:30:42 +0200, Vinzent 'Gadget' Hoefler
<nntp-2004-05@t-domaingrabbing.de> wrote:

>Dmitry A. Kazakov wrote:
>
>>On Thu, 06 May 2004 11:41:11 +0200, Vinzent 'Gadget' Hoefler
>><nntp-2004-05@t-domaingrabbing.de> wrote:
>>
>>>Dmitry A. Kazakov wrote:
>>>
>>>>Why that should be told? I'd say that "with" is superfluous.
>>>
>>>No! If at all then it is "use" which is superfluous. ;-)
>>
>>How so? "Use" has some semantical sense. It changes visibility. You
>>might claim that this is not necessary, but that would be another
>>story. On the contrary "with" has no other sense than being just a
>>hint to the compiler/linker.
>
>And a idea to me which packages another one is using.

Either you agree on that IDE could tell you that better, or I would
claim that all packages with-ed implicitly should be made explicit!
(:-))

>This is
>especially useful with some of the more "evil" parts of Ada like
>Unchecked_Conversion. :)

Then it it should be "without"!

BTW Ada will now have a notion of profile (like Ravenscar). It would
be nice to have an ability to define a profile, a contract of using
some definite subset of Ada. Like one without instantiations of
Unchecked_Conversion.

>>It could well be just a pragma, like the
>>elaboration control ones.
>
>Yes. Or like the C pragmas that tells the Preprocessor which files it
>should include to get all the prototype-declarations. Well, sometimes
>it even works without these, yes. Do you really *want* it to work in a
>similar way? I don't.

ARM does not specify how unit library works. So even if you write
"with X", it does not warranty that X will be with-ed, especially when
it is not in the library. (:-)) You have to set up the project, use -I
key in gnatmake etc. The point is, if this work has to be done in one
place, why should it be repeated in the source again?

>(BTW, for that discussion it might be funny to note that these days
>even more and more of the C++-folks consider "using some_namespace;"
>to be evil. And now we want to encourage to do exactly the opposite of
>that in Ada?)

Because Ada was designed with "use" in mind! The difference is that
Ada allows view management. To drop this idea, essential for building
and maintaining large layered system, just because of a moss-grown
language where types and subroutines are global, that would be at
least unwise.

>For me it is still the same principle: Make something as local as you
>can. No matter if it is a variable, a procedure, ... or a namespace.

I didn't object this principle.

>>Then semantics of renaming is inconsitent with one of "use", or better
>>to say, simply inconsistent. This is the source of numerous problems:
>>
>>with Ada.IO_Exceptions;
>>package A is
>>   End_Error : exception renames Ada.IO_Exceptions.End_Error;
>>   X_Error : exception;
>>end A;
>>--------
>>with A;
>>package B renames A;
>>--------
>>with A; use A;
>>with B; use B;
>>with Ada.IO_Exceptions; use Ada.IO_Exceptions;
>>procedure C is
>>begin
>>   ...
>>exception
>>   when X_Error =>
>>      -- This is OK, multiple views of same thing
>>      ...
>>   when End_Error =>
>>      -- This is illegal, viewing two different views of one thing!
>>      ...
>>end C;
>
>See. That's a perfect example for a "use"-Problem, which I simply want
>to avoid (and which I want to do consistently):

No, "use" is consistent. When you use something twice, that does not
create additional views. What is inconsistent, is that renaming of an
exception creates a view colliding with a view of the renamed thing.

[...]

>I don't know what this has to do with renaming. If you'd declare
>End_Error separately in the packages you would run into the same
>problem, so in fact it is a "use" problem.

>Well, you might argue, just because you renamed it and thus in fact is
>exactly the same,

Yes I do.

>the compiler could figure this out by itself. But if
>it would really do that, it then would be me to call this behaviour
>inconsistent.

Don't you agree that there is a difference between views and viewed
things? How could names indicating the same thing conflict? What is
overloaded here to cause the conflict? What is the sense of the
conflict? Something unresolved, ambiguous, what? 

>>>It's much more simple: Never use "use". :)
>>
>>Once I will become a rich man, I will buy a LCD with horizontal
>>resolution of 10240 pixels, install small fonts, get spectacles ...
>>(:-))
>
>Considering I don't use "use" globally[0] and even restrict myself to
>72 columns, I don't really understand that part of the problem. :)

There is no problem. Just if you were consistently against any view
management, then you should have gone further:

"Never use child packages, they are globally using their parents!"

--
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de