Re: Elaboration order handling (Was: Bug in 'gnatmake')

[Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>]

On 06/21/2013 12:10 PM, Robert A Duff wrote:
 >
 > Interesting.  You are very close to agreeing with me that statements and
> declarations are more-or-less the same thing (syntactically), and
> wherever one is allowed, so should the other.  What's wrong with
> statements in a package spec (or body decl part)?  If you allow "null;"
> in a declarative part, then why not allow an assignment statement, or a
> procedure call?  And if you do that, there's no point at all to the
> "begin" that appears in the middle of a procedure body.

I've seen code in languages that allow mixing of declarations and executable 
statements, and I didn't like it. Maybe this is because I'm used to Ada (and 
Pascal before it), but I found it difficult to find a declaration when I needed 
to. (Tools can help, but are not always available; since I don't use these 
languages, I wasn't using tools when I looked at them.)

> Once in a while, I want to initialize an object using statements,
> because the "X: T := ...;" syntax doesn't work for some reason.
>
>      package body P is
>          X : ...;
>
>          package Dummy is end;
>          package body Dummy is
>          begin
>              for I in ... loop
>                  X(I) := ...;
>              end loop;
>          end Dummy;
>          ... -- 1000 more lines of code
>
> That extra Dummy package doesn't aid readability.  The other choice,
> moving the initialization way down into the "begin...end P;" part
> is also bad, because the initialization is far away from the
> declaration, and there's lots of opportunity to use uninitialized
> variables in between.

The "X : T := ...;" syntax almost always works if the initialization expression 
is a function call:

package body P is
    function Initialize_X return T is ...

    X : T := Initialize_X;

I built some default-initialized types with fairly complex initialization in 
Ada-83 using such functions, which is why I didn't think Ada-95 really needed 
user-defined initialization. Finalization was another matter.

-- 
Jeff Carter
"Sheriff murdered, crops burned, stores looted,
people stampeded, and cattle raped."
Blazing Saddles
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