Re: Localized Variable Declaration

[Darren New <dnew@san.rr.com>]

David Rasmussen wrote:
> I admit that in this simple example, the second looks simpler,

I would suggest that this would likely be the case for all sufficiently
simple examples, and that if your example is too complex for this to be
true, you probably want to close the scope in which the declaration occurs
before you get to the end of the function.

For example, if I have a 100-line function, and I use variable Page_Length
in lines 25-35 and variable Footnote_Count in lines 55 thru 70, chances are
I don't want Page_Length to still be in scope while I'm calculating
Footnote_Count. On the other hand, if I have a 10-line function, having all
the variables in scope at once makes sense.

The problem is that when you get a function large enough that
all-declarations-at-the-front is too confusing, you want keywords for
finding just where you've declared and initialized all these internal
variables.

Of course, your example might best be written as 

procedure .... is
  begin
    put_line("write two numbers");
    declare
      a : integer := read(...);
      b : integer := read(...);
      c : float := a * b * 42.42;
    begin
      put_line("answer = " & c'img);
    end;
  end;

or maybe something vaguely like that. :-)

Note also that in C, every set of braces introduces a new scope, so
something like
  while (yadda) {
    int i;
    i = blah(); yadda = blah2();
  }
means that i gets created and destructed each time thru the loop. This is
not the case in Ada, so it's not obvious what the equivalent in Ada would
be.

loop
  d : some_controlled_type := blah(25);
  exit when d.should_exit;
end;

Overall, it just seems more confusing than helpful to *me* if you were to
make every loop, then-part, else-part, case label, etc be a declarative
scope.
-- 
Darren New 
San Diego, CA, USA (PST). Cryptokeys on demand.
** http://home.san.rr.com/dnew/DNResume.html **
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