Re: Mutable parameter of a function (long ago was: Re: What evil would happen?)

["Randy Brukardt" <randy@rrsoftware.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
news:bt8vap$455n1$1@ID-77047.news.uni-berlin.de...
...
> The point is that the code reader should see that the random generator is
> not a pure function of its argument. This has to be seen immediately from
> the specifications, not from a speculation "how-I-would-implement-that".
> This is why either the parameter has to be an access or an in-out.
Anything
> other is wrong, IMO. Similarly the way the operations on File_Type were
> declared is IMO wrong!

You're probably right, but that isn't the model of Ada.

In parameters and constants just provide a constant view of an object. But
nearly every object has a variable view as well -- you just can't explicitly
name it. Initialization and finalization are always done on a variable view
of the object - even if it is declared as a constant.

That will be more obvious in Ada 200Y, because of the ability to initialize
limited objects. A constant of a limited type might contain a task;
certainly that task will run and modify its local objects without any regard
to whether it is declared in a constant or variable. The task will have a
variable view of its containing object, even if the program as a whole only
has a constant view of the object.

                       Randy.