Indentation

Indentation

[Victor Porton]

What should be the indentation in the following Ada code fragment 
(especially its last line)?

type T is
record
X: Integer;
end record
with Convention => C;

-- 
Victor Porton - http://portonvictor.org

Re: Indentation

[Adam Beneschan]

On Friday, August 8, 2014 9:12:55 AM UTC-7, Victor Porton wrote:
> What should be the indentation in the following Ada code fragment 
> 
> (especially its last line)?
> 
> 
> 
> type T is 
> record
> X: Integer;
> end record
> with Convention => C;

An RM example in B.3.3 looks like:

type T (Flag : Boolean := False) is
    record
        case Flag is
            when False =>
                F1 : Float := 0.0;
            when True =>
                F2 : Integer := 0;
        end case;
    end record
    with Unchecked_Union;

That's as good an answer as you're going to get.  Other people may have other preferences, but you really can't make an objective case for one or another style as long as it's reasonable.

                              -- Adam

Re: Indentation

[Jeffrey Carter]

On 08/08/2014 09:32 AM, Adam Beneschan wrote:
>
> An RM example in B.3.3 looks like:
>
> type T (Flag : Boolean := False) is
>      record
>          case Flag is
>              when False =>
>                  F1 : Float := 0.0;
>              when True =>
>                  F2 : Integer := 0;
>          end case;
>      end record
>      with Unchecked_Union;
>
> That's as good an answer as you're going to get.  Other people may have other preferences, but you really can't make an objective case for one or another style as long as it's reasonable.

That depends on whether people can agree on a precise specification of why 
indentation is used. The compiler doesn't care, so it must be for humans, and as 
it increases writing complexity, it must be for readers. So if we have a precise 
statement of what indentation is supposed to convey to readers we can speak more 
objectively about it than just "this is what I like" or "this is what the ARM uses".

For me, indentation exists to reflect nesting. If A is indented 1 indentation 
level from B, then A is nested directly within B; if A is indented 2 levels, 
then it is nested directly in something else (C) that is nested directly within B.

With this definition, the indentation in the ARM example is clearly incorrect. 
The case statement is nested directly within the type declaration, but is 
indented 2 levels; F1 and F2 are nested directly within the case statement but 
are indented another 2 levels.

What is new in Ada 12 that I haven't worked with yet is the aspect clause. This 
is clearly part of the type declaration, not nested within it, and so should be 
part of the type framing text. So I would probably indent this as

type T (Flag : Boolean := False) is record
    case Flag is
    when False =>
       F1 : Float := 0.0;
    when True =>
       F2 : Integer := 0;
    end case;
end record with Unchecked_Union;

For a lengthy aspect clause, I like something that indicates clearly that the 
declaration is not finished yet, so I'd probably use

end record with
    <aspect 1>,
    <aspect 2>,
    ...,
    <aspect N>;

I've never heard a reason for indentation that resulted in the indentation used 
by the ARM, or a satisfactory explanation of why the ARM indents record type 
declarations and case statements the way it does. If one should write

type T is
    record

then surely one should also write

type T is
    range

type T is
    array

and the like.

At the Ada launch (1980 Dec 10), Ichbiah talked about "comb structures" driving 
the layout of code, and the ARM indentation of records and cases seems to 
violate that rule.

Of course, the ARM indentation goes back to Ada 80, and one can argue that the 
ARM is never wrong, in which case indentation is arbitrary and the only rule can 
be "use what the ARM uses".

-- 
Jeff Carter
"We call your door-opening request a silly thing."
Monty Python & the Holy Grail
17

Re: Indentation

[Peter Chapin]

On 2014-08-08 13:16, Jeffrey Carter wrote:

> What is new in Ada 12 that I haven't worked with yet is the aspect
> clause. This is clearly part of the type declaration, not nested within
> it, and so should be part of the type framing text. So I would probably
> indent this as
> 
> type T (Flag : Boolean := False) is record
>    case Flag is
>    when False =>
>       F1 : Float := 0.0;
>    when True =>
>       F2 : Integer := 0;
>    end case;
> end record with Unchecked_Union;

To my mind the aspects should be introduced on a separate line so they
aren't lost. I had to review the declaration above a couple of times
before I realized the aspect was even there.

I favor indenting the aspect. Consider the common case where there are
multiple declarations at the same level

   type X_Type is ...;
   type Y_Type is ...;
   procedure A(...);
   function B(...) return ...;

If you slip an aspect in at the same level of indentation as the
declaration to which it is attached it clutters things considerably.

   type X_Type is ...
   with ...;
   type Y_Type is ...
   with ...;
   procedure A(...)
   with ...;
   function B(...) return ...
   with ...;

Of course adding some blank likes would help but I still like to see the
aspect set off so its association with the previous declaration is obvious

   type X_Type is...
     with ...;
   type Y_Type is ...
     with ...;
   procedure A(...)
     with ...;
   function B(...) return ...
     with ...;

Peter

Re: Indentation

[Peter Chapin]

On 2014-08-08 13:45, Peter Chapin wrote:

> I favor indenting the aspect. Consider the common case where there are
> multiple declarations at the same level...

I forgot to mention (sorry) that if the aspect's value is complex, such
as often the case for Pre, Post, and other assertions, it is normal for
the aspect itself to span multiple lines. Trying to put it on the same
line as the declaration is crazy in that case and not indenting it
doesn't work well either. Then, for consistency it seems natural to
treat all aspects the same way.

   -- Division returns quotient and remainder.
   procedure Divide (Dividend  : in  Very_Long;
                     Divisor   : in  Very_Long;
                     Quotient  : out Very_Long;
                     Remainder : out Very_Long)
      with
         Depends => (Quotient  => (Dividend, Divisor, Quotient),
                     Remainder => (Dividend, Divisor, Remainder)),
         Pre     => (not Is_Zero(Divisor)) and
                    (Divisor.Digit_Length  = Remainder.Digit_Length) and
                    (Dividend.Digit_Length = Quotient.Digit_Length ) and
                    (Dividend.Digit_Length = 2*Divisor.Digit_Length);

Peter

Re: Indentation

[Randy Brukardt]

"Jeffrey Carter" <spam.jrcarter.not@spam.not.acm.org> wrote in message 
news:ls30lf$cj2$2@dont-email.me...
...
> Of course, the ARM indentation goes back to Ada 80, and one can argue that 
> the ARM is never wrong, in which case indentation is arbitrary and the 
> only rule can be "use what the ARM uses".

My understanding is that the Ada 9x team went through the entire standard 
and regularized the indentation. (It's not really from Ada 80 anymore.) 
Remember, they also switched to Title case identifiers (Ada 83 had them all 
in UPPER CASE - yuck!). Since, we pretty much take it as given.

For aspects, we had a long and rather inconclusive discussion about how they 
ought to be indented. The style shown in the RM is what we settled on, but 
it wasn't close to unanimous.

The only indentation that I know I do differently than the RM is record 
types (I think the RM inserts an extra level there for no reason). 
Otherwise, I follow the RM style pretty closely (more closely as the years 
go by).

                                    Randy.

Re: Indentation

[Pascal Obry]

Le vendredi 08 août 2014 à 19:12 +0300, Victor Porton a écrit : 
> What should be the indentation in the following Ada code fragment 
> (especially its last line)?
> 
> type T is
> record
> X: Integer;
> end record
> with Convention => C;

For me:

type T is record
   X: Integer;
end record with Convention => C;

3 lines. If there is multiple aspects, probably:

type T is record
   X: Integer;
end record with 
  Pass_By_Copy => True,
  Convention   => C;

or

type T is record
   X: Integer;
end record 
with 
  Pass_By_Copy => True,
  Convention   => C;

Not sure yet as this is quite recent and I did not use such aspects.

-- 
  Pascal Obry /  Magny Les Hameaux (78)

  The best way to travel is by means of imagination

  http://v2p.fr.eu.org
  http://www.obry.net

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