Re: Ada style of passing 'in' parameters considered dangerous?

[Richard Riehle <richard@adaworks.com>]

Robert A Duff wrote:

> How about this example:
>
> We have a record representing fractions of whole numbers:
>
>     type Fraction is
>         record
>             Numerator: Integer;
>             Denominator: Positive;
>         end record;
>
>     procedure Reciprocal(Result: out Fraction; X: Fraction);
>     -- Sets Result to the reciprocal of X.
>
>     procedure Reciprocal(Result: out Fraction; X: Fraction) is
>     begin
>         if X.Numerator > 0 then
>             Result.Numerator := X.Denominator;
>             Result.Denominator := X.Numerator;
>         ... etc
>
> It seems reasonable (without seeing the body of Reciprocal) to do:
>
>     Reciprocal(Foo, Foo);

Interesting example.   A little bit of a stretch since it would rarely
occur in practice.  However, it is one reason why I proposed, a few
years ago that we add a mode based on the reserved word constant.
In particular, I would like to be able to use that reserved word
anywhere we normally would be allowed to use access.  Your
example suggests it might be useful under other circumstances
as well.

Richard Riehle